science skills stages 4-6(2)

8/7/2019 Science Skills Stages 4-6(2)

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KNOX GRAMMAR SCHOOL

SCIENCE DEPARTMENT

SCIENCE SKILLS

STAGES 4-6


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Contents

Section Page

Graphing Data Sets 3

Data Tables 9

Scientific Diagrams 10

Flow Charts 11

Practical Reports 13

Experiments Essential Terms 15

Reporting First Hand Investigations in Exams 17

Standard Laboratory Practice 18

Secondary Source Investigations Essential Terms 19

Scientific Method 20

Stage 6 Prescribed Focus Area and Skills 22

Appendix Extra Notes 24

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Equipment

Pen, pencil, eraser, ruler (and protractor for sector graphs)

Checkpoints

This list provides dot point guidelines for marking graphs in Science.

1. Graphs should be done on graph paper.

2. All graphs should have a title that reflects the purpose of the graph

3. The independent variable should be on the X axis & dependent variable on the Y axis.

4. The X axis and Y axis are labelled with appropriate variables.

5. The X axis and Y axis have appropriate units

6. The X axis and Y axis have appropriate/uniform scales

7. Aim to use at least 80% of the graph paper to ensure greater accuracy when making readingsand measurements off the graph.

8. The points are plotted accurately with a small x.

9. The appropriate graph has been drawn (column, line, histogram, sector or divided bar)

10.Every component of the graph is to be done in pencil. This includes all labelling.

Variables ,Axes and Plots Drawn with a ruler in pencil Label each axis with the name of the variable and the units the variable is measured in. The

units should have brackets around them. The independent variable is the one you change and always goes on the horizontal axis (x

axis). For example if you are heating water and measuring the temperature every 30 s until itboils, time is the independent variable because that is the variable you changed.

The dependent variable is the variable you are measuring and goes on the vertical axis (yaxis). For example if you are heating water and measuring temperature of every 30 s until itboils, temperature is the dependent variable because that is the variable you are measuring.

Ensure the scale you use will allow for a full range of measurements, covering the smallest andhighest values of your data.

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GRAPHING DATA

Temperature (C)

Time (min)


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Scales are to be evenly spaced and increase upward and from left to right. Use reasonablescales for each axis eg multiples of 1,2,5 or 10.

Only plot the points for data provided unless directed to do differently in the question.LINE GRAPH

A Line Graph if the independent variable is not grouped but continuous and the graph can be usedto find the relationship between variables (Watson 1994 p39). A line graph is therefore used to showhow one variable will affect another (Oldum 2008 p100). The independent variable can have any

value such as length, height, weight and mass.

Example 1 (Oldum 2008 p101).

Draw a line graph for the data showing the speed of a car that started from rest in the table below.

Time

(seconds)

Speed

(m/s)0 0.0

2 1.4

4 2.6

6 4.4

8 5.6

10 6.6

12 8.2

14 9.6

Example 2 (2001 School certificate Exam)

Draw a graph to show the time taken for a vitamin tablet to dissolve in 200mL of water at differenttemperatures.

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Temp200mLwater(C)

Time todissolve

(s)

10 120

15 60

25 40

50 20

90 10

Note: In this

graph and the

others below,

very small

crosses have

been used as

plots.


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COLUMN GRAPH

A Column Graph is used if the independent variable values are specific; that is groups of thingshave been counted or measured(Watson 1994 p39). The height of the column shows the numberin the count (Oldum 2008 p101). Column graphs are therefore used to compare things and the

columns are in order, either increasing size or decreasing size.

A Bar Graph is used if the independent variable values are specific; that is groups of things havebeen counted or measured(Watson 1994 p39). The length of the horizontal bar shows the numberin the count (Oldum 2008 p101). Bar graphs are therefore used to compare things.

Example Column (Oldum 2008 p101).

Animal Heart Rate(beats/min

)

camel 35

horse 41

human 70

rabbit 210

mouse 670

rat 750

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HISTOGRAM

A Histogram is similar to a column graph but the columns should touch each other, showing eachcolumn has the same type of data:. (Oldum 2008 p101). Histograms are therefore used to compare

things and the columns do not get arranged in increasing size or decreasing size.

Example (Oldum 2008 p101).

Month AverageTemperatur

e(C)

March 25

April 23

May 22June 19

July 17

August 18

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SECTOR AND DIVIDED BAR GRAPHS

A sector (or pie) graph and divided bar graphs are used to show the percentage composition of

different categories that are not affected by each other.(Oldum 2008 p102).

When drawing a sector graph, a protractor must be used.

Sector (Oldum 2008 p102).

Gases in theatmosphere

PercentageVolume

nitrogen 78

oxygen 21argon 0.9

others 0.1

Notes:

A protractor must be used.

Moving clockwise, the sectors are positionedfrom largest to smallest.

Divided Bar Graph (Watson 1994 p39).

Sample Percentage Composition

Iron Silicondioxide

Aluminiumoxide

Others

A 40 10 20 30B 50 5 5 40

C 55 5 10 30

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Some things to be aware of in Stage 6 graphs:

Extrapolation extend the graph using a dotted line.

Interpolation always show working on the graph to show how the value was determined.

Ignore all outliers when determining the best way to connect the plotted points. To maximize the space on the grid, an axis does not have to start at zero. To start at a

number other than zero two parallel lines can be used at the start of the axis.

Graph 1 note the interpolation

Graph 2 note the extrapolation

References

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Time(seconds)

Speed(m/s)

0 0

2 1.44 2.6

5 ??

6 4.4

8 5.6

10 6.6

12 8.2

14 9.6

Mass(g)

Stretch(mm)

0 0

10 5

20 10

30 2540 20

50 26

60 29

70 33

80 ??

90 ??


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Oldum, C. (2008). Understanding Science for Years 9 and 10. Oldum and Garner, Sydney.Stannard, P., Williamson, K. (2006). Science World 7. Macmillan Education, South Yarra.Watson, C. (1994). Processes Science in Action. Rigby Heinemann, Port Melbourne.

This list provides dot point guidelines for marking graphs in Science.

1. Title that reflects contents of the results table

2. The table is enclosed and contains neat straight lines

3. Where appropriate, the Dependent Variable appears across the top of the table

4. Where appropriate, the Independent Variable appears down the side of the table

5. Appropriate units are listed in column and/or row headings but not in the body of the table.

6. Multiple measurements are taken and averages calculated.

7. A data table goes in the results section. All relevant information should be written within thetable.

EXAMPLE 1

METAL

Volume of Hydrogen Gas collected (mL)

HCl

0.5 mol/L

HCl

1.0 mol/L

HCl

2.0 mol/L

HCl

4.0 mol/LMagnesium 5 10 20 40

Zinc 2 5 12 22

Iron 0 1 5 10

Copper 0 0 0 0

EXAMPLE 2

Maximum Diameter of Crater

Drop Ht (m)Diam 1

(mm)

Diam 2

(mm)

Diam 3

(mm)

Diam 4

(mm)

Diam 5

(mm)

Av. Diam

(mm)

Height 1 1 m 120 130 145 112 138 129

Height 2 2 m 125 135 150 117 143 134

Height 3 3 m 130 140 155 122 148 139

Height 4 4 m 135 145 160 127 153 144

Height 5 5 m 140 150 165 132 158 149

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DATA


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This list provides dot point guidelines for marking diagrams in Science.

1. Diagrams must be done in pencil.

2. Diagrams must have a heading.

3. Scientific diagrams are always done 2 dimensionally (cross section) and a ruler must be usedfor all straight lines.

4. The diagram is to be large and all components must be in proportion.

5. No lines are to be drawn across the top of glassware or where liquid is to pass through.

6. All components of the diagram must be labelled (in pencil) and labels are to be clear and thearrow head is to touch identified object.

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SCIENTIFIC


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ReferenceOdlum, C., Garner, R. (2008). Understanding Science for Years 9 and 10. Odlum and Garner Publishing, Sydney.

This provides guidelines for the construction of flow charts in Science.

Should be presented as an easy to understand diagram showing how the steps in a process fit

together.

Sequence of the steps or pathways in the process must be clear and sequential.

Flow charts usually contain three main types of symbols that have a special shape and use.

The entire flowchart including headings, labels and writing are to be done in pencil.

Elongated circles These represent the start or end of the process.

Rectangles These indicate steps that are instructions or actions.

Diamonds These occur in the flow chart at points where decisions must be made.

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FLOW

FinishStart

This is what you should donow or this is the next step

Make a decisionhere


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Other important points:

Text in each symbol must be appropriate to the purpose of the direction,

Symbols are connected by arrows showing the flow of the process.

All this information on flow charts is taken fromCurriculum Support for Teaching Science 7-12, Volume 14 No. 1, 2009 www.curriculumsupport.education.nsw.gov.au[accessed 19 January 2010.

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http://www.curriculumsupport.education.nsw.gov.au/http://www.curriculumsupport.education.nsw.gov.au/


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This provides guidelines for the writing and marking of practical reports in Science.

Set out methodically, in a format that is possible for another person to easily follow and repeat

the experiment without having to guess any steps.

Should be written in third person and in past tense.

Includes diagrams of apparatus set up. Tabulate data and use graphs where possible.

The following sub-headings are to be used:

Aim: Brief, one sentence statement of the purpose of each experiment; what is the experiment

setting out to discover. An aim should (in most cases) start with To.

Hypothesis:

A proposed single sentence statement as to the outcome of the investigation.

Must be written in the third person.

Must relate to the aim.

Shows a statement that can be tested and does not try to explain why by using the

scaffold If ......... then ................

Equipment: A list of equipment used. Be specific and quantitative where possible.eg 100mL beaker,

not just beaker.

Method:

Must be sufficiently detailed so the experiment can be repeated exactly, without having

been seen.

It should be concise point form, in the third person, past tense and in report style writing.

Risk Assessment:This should be tabulated with the following headings

Identify Assess Control

Identify the nature of thehazard.eg hydrochloric acid

How likely is it to occur?When would it occur? Usecorrect terminology

How do I stop it fromoccurring? What do I do ifit occurs?

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PRACTICAL


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eg The acid is corrosiveand will burn the skin.

eg Use a dropper anddeliver the aciddropwise

Scientific Set-Up Diagram: Clear scientific diagram (not a sketch) using a ruler and a pencil with labelling. Refer

guidelines on Scientific Diagrams

Results: Data should be presented in a table. There is to be no writing outside the boundaries of the

data table.

All observations made during the experiment should be recorded here.

Discussion:

Answer questions and discuss if the experiment was suitable.

The suitability of the experiment should be addressed by assessing the reliability, accuracy

and validity.

Discuss any modifications that need to be made by changing the method or apparatus and

compare the results with accepted values (if possible).

Conclusion: Brief, one sentence statement stating the outcome of the investigation in relation to the aim.

Where possible should be quantitative.

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Independent Variable:A factor in an experiment that is changed and affects the final outcome of the experiment. Theindependent variable will always go on the horizontal axis of a graph.

Dependent Variable:A factor which changes during an experiment (variable), as a result of the experiment. It is theobserved or measured outcome that depends on the other factors that have been changed in theexperiment. The dependent variable will always go on the vertical axis of a graph.

Controlled Variables:A controlled variable is something in an experiment that doesn't change between trials. For example,when testing the expansion of metals at certain temperatures, a controlled variable might be keepingthe pressure on the metals consistent.

Experimental Control:

A control is a standard used for comparison of results to ensure the results achieved are due to theindependent variable. Therefore, the control experiment is identical to the test experiments, exceptthe INDEPENDENT variable is not included. In experiments where a control is possible (a control isnot possible in some experiments), it must be included.

Validity:The extent to which the processes and resultant data measure what was intended. A validexperiment measures only the effects of the independent variable(s) on the dependent variable(variable of interest) with all other variables held constant. Remember an experiment usually hasthree kinds of variables: independent, dependent, and controlled. To ensure a fair test, a goodexperiment has only one independent variable. As the scientist changes the independent variable, heor she observes what happens.

Reliability:The degree with which repeated observation and/or measurements taken under identicalcircumstances will yield the same results. Reliability is improved by repetition (doing more trials)and will ensure the trustworthy-ness of the results. Random errors associated with how theexperimenter carries out the measurements should be considered when assessing reliability.

Accuracy:An accurate experiment gives exact results that are as close to the ideal (data book) ortrue value

as possible. Systematicerrors associated with the experimental setup should be considered whenassessing accuracy.

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EXPERIMENTS ESSENTIAL


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For more reading on validity, reliability and accuracy in relation to experiment reports, refer toAppendix.

Variables

Aim of Experiment

Variables

Which Variable will you test?

This is the INDEPENDENT VARIABLE

Which Variable will make up your results?

This is the DEPENDENT VARIABLE

To make this a FAIR TEST, which Variables are kept the same?

These are yourCONTROLLED VARIABLES

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In most exams, students will be asked to design a method for a first-hand investigation or report onone they conducted as a mandatory practical. The following provides a scaffold on which to preparean answer and provides a dot point guideline for marking these questions in Science Exams at Knox.

Example (from 2007 SC exam)

A scientist carried out a controlled experiment to test the following hypothesis

Cane toads are attracted to UV light

Describe a method for a controlled experiment to test this hypothesis.

Sample Answer

Construct (or collect) 10 animal traps that are able to fit a UV light source. Ensure the trapsare all the same size and shape.

Risk Assessment:

Identify electricity to operate UV lamps,

Assess electricity in the open, especially when moisture is present can causeelectrocution,

Control use UV lamps that are battery operated. In an area populated by cane toads, set the traps at an even distance apart.

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REPORTING FIRST HAND INVESTIGATIONS IN

Answer Plan:

Safety. Document risk assessment. Identify, Assess, Control.

Equipment use correct names. Can be incorporated into the method.

Use of a control.

Variables. Be quantitative and demonstrate a fair test by showingvariables that need to be controlled. Show how results will becollected and all units of measurement.

Identify the dependent variable and the independent variable. Repetition average Method - Logical flow, plus use of correct scientific terms such as


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Into 5 traps place a UV light source. Ensure the lamps and battery power are identical toget the same intensity of light.

Into the other 5 traps place a normal light source, again ensuring the lamps and batterypower are identical to get the same intensity of light. This is the CONTROL.

Leave the traps set up from 8pm to midnight.

Count the number of cane toads in each trap and record this number.

Repeat the experiment every night for a week.

The following is a dot point guideline indicating how students should carry out allexperiments.

Students are to be aware of how the Risk Assessment matrix works. This can be found as aposter in each lab.

Students must listen carefully to the safety briefing given out at the start of each lesson whichwill also include correct disposal of chemicals. The teacher will use the risk assessmentissued with each experiment to do this.

Safety glasses must be worn for the duration of all experiments.

The only experiment to be carried out is the one directed by the teacher.

Laboratory rules must be obeyed at all times.

No more than 2 students per group. Each group to work independently, unless instructedotherwise by the teacher.

Students are to be familiar with the laboratory and know where all equipment is, especially

safety equipment (eg eye wash, fire blanket) All equipment is to go back in the correct place and work area is to be left tidy and all gas

stopcocks checked to ensure they are off. Any breakages or damaged equipment must bereported to the teacher.

All glassware must be cleaned and placed in draining rack.

No solid material is to be placed in sinks eg matches, nails, metals etc. Solid material is to bedisposed in rubbish bin.

After each experiment hands are to be washed.

No practical materials are to be removed from the laboratory.

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STANDARD LABORATORY


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Validity:How close or inline the information or data is to what the topic/question of interest is about or what isbeing evaluated;

Reliability:Where the source (personal site/extremist view/respected institution) has come from and the detailsindicated in the sources promote the same or similar message/idea/result/definition. Providingappropriate breadth in these similar secondary sources can increase reliability.

Notes:

In assessing validity, you might consider the degree to which evidence supports the assertionon or claim being evaluated. In some cases, you may be able to make observations orconduct experiments to confirm the reliability and validity of the information that you haveidentified.

Research should involve identifying information from a wide range of sources. These shouldinclude educational texts, recent science journals, internet sites and other forms of media.

Personal site may be a wiki

A respected institution will have a web site ending in .gov or .edu or .org

A commercial organisation will have a web site ending in .com

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SECONDARY SOURCE INVESTIGATIONS ESSENTIAL


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The following has been compiled using Science Focus 2. (Whalley, K. , Neville, C. Roberson, P. Rickard, G. (2006).

Science Focus 2. Pearson Education. Melbourne. Australia.)

SCIENTIFIC RESEARCH involves a specific application of the SCIENTIFIC METHOD wherebyinvestigations are carried out in order to acquire new knowledge and provide answers that show anunderstanding of questions that arise from observations.

QUESTION

Idea as an answer to the question becomes an HYPOTHESIS. This is the result of observations and

current knowledge.

Experiments are carried out to test the hypothesis (this will have an aim that relates to thehypothesis). Experimentation is essential in the scientific method. The experiments needs to be validand well designed so the results are accurate. Results will either support the hypothesis or not. If the

results dont support the hypothesis then a new hypothesis needs to be made (this is part of theevaluation process).

If, through further testing, the results support the hypothesis, then this idea can become a THEORYwhich is an explanation of the idea. Theories are supported by evidence and testing.

Theories can lead to MODEL development. These enable scientist to make a clearer description orexplanation of their understanding, especially if the hypothesis is difficult to assess or show easily.

Models develop and research continues resulting in advancements that improve our lives. This isTECHNOLOGY.

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SCIENTIFIC


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When a theory can be applied to a number of areas of scientific research and is always shown to becorrect, then this piece of knowledge and understanding becomes a LAW.

Some further explanation of terms from the scientific method:

Technology refers to the way in which people (and indeed animals) try to improve objects anddevices that are used on a day to day basis to make their operation easier, better and more efficient.Technology and how people benefit from it will vary from person to person and even culture toculture.

Models are a way of explaining scientific phenomena that cant be directly observed because it is toosmall to be seen (eg atoms so use molecular model kits), or too large or complicated to be easilydemonstrated (eg planets moving around the sun or size of planets). A model could be a diagram, acomputer simulation or something constructed.

A society can exist in many different forms as it refers to groups of individuals sharing similar beliefsand values.

When trying to define society), it is useful to think of society as:

the people that make up that society their lives, opinions, living conditions, socialawareness, health, education.

the environment

capital, financial considerations, employment

the possible future growth / changes

Environment is defined as the living and non-living surrounding of an organism

When trying to define environment, it is useful to think of environment as:

all the living organisms and their interactions in that particular area the water and soil

the possible air and climate conditions

how a change can affect this environment (living things, interactions and soil etc)

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Year 12 SCIENCE (Biology)

Note: There is one of these handouts specific for each science discipline.

Basis of the handout to be given to all students in Stage 6.

General

Know every syllabus dot point. In particular, know how to use the scientific terms that are in thedot points. You must develop a routine every night that whereby a few dot points are reviewed.Pay particular attention to the verb word.

When marking your Trial Examination, all staff at Knox will pay particular attention to the areas

flagged on the front two pages of the examiners comments from last years HSC. Note that theinformation given is word for word identical for every Science. Refer Appendix 1. The keypoints are as follows:

Holistic questions must bring into the answer Yr 11 content + all of the Yr 12 syllabus.The trend recently is questions are set so that information from multiple modulesneed to be included in a full mark answer. PFAs and skill knowledge is essential insuch questions.

Dot points, tables etc are to be used in answering qs. No mind dumping and logical well-structured answers will only be achieved through

planning answers and using the space given. Using more space normally indicates amind dump.

If an answer contains irrelevant information, it cant get many marks, regardless howgood the relevant information is.

Prescribed Focus Areas

A common trend over the last few years in the HSC has been to make the PFAs the central part ofmany questions. This is where most students lose their marks through mind dumping. It is importantto apply your knowledge of the subject content through the focus area. The PFAs are the same forall Sciences. They include:

H1 History of scienceH2 Nature and Practice of scienceH3 Applications and uses of science

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STAGE 6 PFAs and


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H4 Implications for society and the environmentH5 Current issues, research and development

Some examples from 2007 HSC to show how PFAs were incorporated into questions.

Physics Q20 (4 marks)

Assess the effects of the development of AC generators on todays society and the environment

Most students will recall everything they know about AC generators. Instead it is important that

todays society and the environmentare not considered as throw away words, instead these wordsshould be used as key sub-headings in the answer.

Senior Science Q27 (6 marks)

Assess the impacts that changes in communication systems have had on society

Most students will focus on communications systems as this is what the dot point is about. Very few,however, will keep relating the changes in communication to the impact on society at the time andeven fewer students will realise that this question has is expecting H1 (history) to be developed intheir answer.

Chemistry Q29(d) (4 marks)

The work of early scientists has increased our understanding of electron transfer reactions. Describethe impact of this work on society.

Most students recalled very well the work of Galvani, Volta, Davy and Faraday and wrote pages ofcorrect information. This score one out of 4. However, the focus of this question was impact on

society. By relating the work of these four to electricity and simply saying something like Electricityprovides us with the ability to heat our homes, see in the dark and have portable music and thispositively benefits people in their everyday life has shown an impact on society and moves theanswer into the top marking bracket.

Biology Q24 (6 marks)

The flowchart shows the development of technology used to measure oxygen

EES Q23 (5 marks)

How has technology improved our understanding of fossil life-forms?

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Regardless of the science being studied, there are key words that must be able to be defined andused in any of the key content areas (9.2, 9.3, 9.4, Option).

Technology

Scientific thinking

Model, theory, law

Society

Environment

Research

Appendix Extra Notes

Reliability, validity and accuracy what do they mean?

In relation to secondary source investigations -

Collecting data from secondary sources:

When you have to assess the reliability and validity of information and data from secondary sources,

the best procedure is to make comparisons between data and claims of a number ofreputable

sources.

In assessing validity, you might consider the degree to which evidence supports the assertion on or

claim being evaluated. In some cases, you may be able to make observations or conduct

experiments to confirm the reliability and validity of the information that you have identified.

Research should involve identifying information from a wide range of sources. These should include

educational texts, recent science journals, internet sites and other forms of media.

When choosing the secondary sources of information that are most relevant, consider:

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Validity = how close or inline the information or data is to what the topic/question

of interest is about or what is being evaluated;

Reliability = where the source (personal site/extremist view/respected institution)

has come from and the details indicated in the sources promote the same or similar

message/idea/result/definition. Providing appropriate breadth in these similar

secondary sources can increase reliability.


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In relation to first hand investigations -

In the context of you planning first hand investigations, issues related to accuracy, reliability and

validity do impact on the choice of the measuring device and how confident you are about the

conclusions drawn from the results of the investigations. It is easier to be confident of your

conclusion in any investigation when there are limited variables involved and where these variables

are controlled.

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1. Validity of first hand data in experiments The extent to which the processes and

resultant data measure what was intended. A valid experiment measures only the effects of

the independent variable(s) on the dependent variable (variable of interest) with all

other variables held constant. Remember an experiment usually has three kinds of

variables: independent, dependent, and controlled. To ensure a fair test, a good experiment

has only one independent variable. As the scientist changes the independent variable, he or

she observes what happens.

2. Reliability of first hand data in experiments- The degree with which repeated

observation and/or measurements taken under identical circumstances will yield the same

results. Reliability is improved by repetition (doing more trials) and will ensure the

trustworthy-ness of the results. Random errors associated with how the experimenter

carries out the measurements should be considered when assessing reliability.

3. Accuracy of first hand data in experiments An accurate experiment gives exact

results that are as close to the ideal (data book) ortrue value as possible. Systematic

errors associated with the experimental setup should be considered when assessing

accuracy.


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The need foraccuracy of data should influence the choice of equipment for conducting first hand

investigations.

We can assess accuracy by:

(i) Examining how exact the measurement is from the data book/true value and display a

percentage difference , %diff = ((true value exp value)/true value x 100/1);

(ii) Considering systematic errors are related directly to the experimental setup. Changes in

the setup may improve the accuracy of the result. The precision of a measuring device

(smaller limit of reading) may improve the accuracy of the final result.

(iii) Stating the estimated uncertainty or implicitly by the number of significant figures given.

Remember that accurate measurements do not ensure an experiment as valid or reliable

The relationship between validity and reliability can be confusing. Measurements and other

observations can be reliable without being valid. A faulty measuring device can consistently provide a

wrong value therefore providing reliably incorrect results.

We can assess validity by:

(i) Examining the variables and how they have been controlled. In other words, how well is

the experiment designed? The experiment can be more valid by refining the design of the

experiment and the procedure/method used. Reducing the complexities in the range of

variables that need to be controlled can allow for more valid results;

(ii) Considering whether the experiment measures the variable of interest.

We can assess reliability by:

(i) Completing the experiment many times (at least three trials of a specific measurement)

and checking that the results are repeatable;

(ii) Considering random errors are related directly to the experimental technique. These errors

can be reduced by increasing the number of trials, plotting data and removing outliers,

averaging numerically or using graphical techniques. Other examples related to random

errors include parallax error (viewing scales at eye level and placing measuring device on

level surface) and resetting or zeroing a measuring device.

It is important to point out that by increasing repetition and precision may not increase the accuracyin the data collected. As stated above, a faulty piece of equipment that has a high precision may

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provide reliably incorrect values (when compared to the true value) throughout the experiment.

Furthermore, measurements and observations cannot be valid unless they are reliable and accurate.

In summary,

ACCURACY = Exactness or conformity to truth.

RELIABILITY = Repeatability or consistency. A reliable experiment is one that if repeated many

times will produce identical results.

VALIDITY = An experiment that fairly tests the hypothesis. An unreliable experiment must be

inaccurate and invalid, as a valid scientific experiment would produce reliable results in multiple trials.

Other information on the above.

The following notes were taken from Optimizing Student Engagement and Results in theQuanta to Quarks Option by Dr Mark Butler, Gosford High School. The full article may be found atthe link below.

http://science.uniserve.edu.au/school/curric/stage6/phys/stw2004/butler.pdf

ACCURACY, RELIABILITY AND VALIDITY

The Board of Studies definitions are very brief and the following expanded definitions may be of use:

a) ACCURACY: Exactness or conformity to truth.

Science texts refer to accuracy in two ways:

(i) Accuracy of a result or experimental procedure can refer to the percentage difference betweenthe experimental result and the accepted value. The stated uncertainty in an experimental resultshould always be greater than this percentage accuracy.

(ii) Accuracy is also associated with the inherent uncertainty in a measurement. We can express theaccuracy of a measurement explicitly by stating the estimated uncertainty or implicitly by the numberof significant figures given. For example, we can measure a small distance with poor accuracy usinga metre rule, or with much greater accuracy using a micrometer. Accurate measurements do notensure an experiment is valid or reliable. For example consider an experiment for finding g in whichthe time for a piece of paper to fall once to the floor is measured very accurately. Clearly thisexperiment would not be valid or reliable (unless it was carried out in vacuum).

b) RELIABILITY: Trustworthy, dependable.

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http://science.uniserve.edu.au/school/curric/stage6/phys/stw2004/butler.pdfhttp://science.uniserve.edu.au/school/curric/stage6/phys/stw2004/butler.pdf


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In terms of first hand investigations the Board seems to define reliability as repeatability orconsistency. If an experiment is repeated many times it will give identical results if it is reliable. Interms of second hand sources reliability refers to how trustworthy the source is. For example theNASA web site would be a more reliable source than a private web page. (This is not to say that allthe data on the site is valid.) The reliability of a site can be assessed by comparing it to several othersites/sources.

c) VALIDITY: Derived correctly from premises already accepted, sound, supported by actual

fact.

A valid experiment is one that fairly tests the hypothesis. In a valid experiment all variables are keptconstant apart from those being investigated, all systematic errors have been eliminated and randomerrors are reduced by taking the mean of multiple measurements. An experiment could producereliable results but be invalid (for example Millikan consistently got the wrong value for the charge ofthe electron because he was working with the wrong coefficient of viscosity for air). An unreliableexperiment must be inaccurate, and invalid as a valid scientific experiment would produce reliableresults in multiple trials.

ERRORS

The two different types oferrorthat can occur in a measured value are:

Systematic error this occurs to the same extent in each one of a series of measurements eg zeroerror, where for instance the needle of a voltmeter is not correctly adjusted to read zero when novoltage is present.

Random error this occurs in any measurement as a result of variations in the measurementtechnique (eg parallax error, limit of reading, etc).

When we report errors in a measured quantity we give either the absolute error, which is the actualsize of the error expressed in the appropriate units or the relative error, which is the absolute errorexpressed as a fraction of the actual measured quantity. Relative errors can also be expressed aspercentage errors. So, for instance, we may have measured the acceleration due to gravity as 9.8m/s2 and determined the error to be 0.2 m/s2. So, we say the absolute errorin the result is 0.2 m/s2

and the relative erroris 0.2 / 9.8 = 0.02 (or 2%). Note relative errors have no units. We would thensay that our experimentally determined value for the acceleration due to gravity is in error by 2% andtherefore lies somewhere between 9.8 0.2 = 9.6 m/s2 and 9.8 + 0.2 = 10.0 m/s2. So we write g =9.8 0.2 m/s2. Note that determination of errors is beyond the scope of the current course.

Consider three experimental determinations ofg, the acceleration due to gravity.

Experiment A Experiment B Experiment C

8.34 0.05 m/s2 9.8 0.2 m/s2 3.5 2.5 m/s2

8.34 0.6% 9.8 2% 3.5 71%

We can say that Experiment A is more reliable (or precise) than Experiment B because its relativeerror is smaller and therefore if the experiment was repeated we would be likely to get a value forg

which is very close to the one already obtained. That is, Experiment A has results that are veryrepeatable (reproducible). Experiment B, however, is much more accurate than Experiment A,

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since its value ofg is much closer to the accepted value. Clearly, Experiment C is neitheraccurate nor reliable.

In terms ofvalidity, we could say that Experiment B is quite valid since its result is very accurateand reasonably reliable repeating the experiment would obtain reasonably similar results.Experiment A is not valid, since its result is inaccurate and Experiment C is invalid since it is bothinaccurate and unreliable.

How do you improve the reliability of an experiment? Clearly, you need to make the experimentalresults highly reproducible. You need to reduce the relative error(or spread) in the results as muchas possible. To do this you must reduce the random errors by: (i) using appropriate measuringinstruments in the correct manner (eg use a micrometer screw gauge rather than a metre ruler tomeasure the diameter of a small ball bearing); and (ii) taking the mean of multiple measurements.

To improve the accuracy and validity of an experiment you need to keep all variables constantother than those being investigated, you must eliminate all systematic errors by careful planning andperformance of the experiment and you must reduce random errors as much as possible by takingthe mean of multiple measurements.

Reliability and validity - what do they mean?

(An article published in Curriculum Support, Science, 2001 Vol. 6 No. 3)

http://74.125.153.132/search?q=cache:e0tpj2thD2kJ:www.curriculumsupport.education.nsw.gov.au/secondary/science/assets/docs/stage4_5docs/s45%2520reliabval.doc+accuracy+reliability+validity&cd=5&hl=en&ct=clnk&gl=au

Reliability and validity are two terms that can be easily confused by students. This becomes an issuewithin Stage 6 syllabuses because students are required to distinguish between them in both first-hand investigations and when using secondary sources (refer to the references from Modules 8.1and 9.1 below).

References to validity and reliability in Stage 6 syllabuses

Skills content 11.2: Plan first-hand investigations to:(c) design investigations that allow valid and reliable data and information to be collected.

Outcome P12: Discusses the validity and reliability of data gathered from first-handinvestigations and secondary sources.

Outcome H12: Evaluates ways in which accuracy and reliability could be improved ininvestigations.

Skills content 12.4: Process information to:(e) assess the reliability of first-hand and secondary information and data by consideringinformation from various sources.

Outcome H14: Assesses the validity of conclusions from gathered data and information.

First-hand investigations

In the context of students planning first-hand investigations, issues related to accuracy, reliability andvalidity will impact on the choice of the measuring device and how confident you are about theconclusions drawn from the results of the investigation.

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A simple example to illustrate the above statement follows.

A student claims that dilute acid reacting with a metal is an example of an exothermic reaction. Yourespond by saying, "OK, let's test that. Get a thermometer, test tube, acid and an iron nail andconvince me."

The student puts 2 cm of acid in the test tube, measures the temperature of the acid (18C) andadds a nail. After about 10 seconds, bubbles form on the nail. After 30 seconds, the thermometerhas not registered any temperature change.

Is the student wrong?

The assumption behind the procedure is that the nail will react with the acid and release enough heatfor the thermometer to detect it. However, the thermometer chosen may not be sensitive enough toshow the temperature change. The more sensitive the measuring device is to changes in theenvironment, the more accurately you can measure the changes.

You repeat the experiment for the student using a temperature probe and data logger. The probe candetect temperature changes as small as 0.2C. After about ten seconds the temperature changepeaks at 0.4C. The student repeats the experiment three times, obtains the same result as you andannounces that the reaction is, as she predicted, exothermic.

The student has confidence in her conclusion because, by repetition, she has established aconsistent pattern of results for the same experiment. Several other students then do the experimentusing different probes and data loggers (same sensitivity as the one used above) and confirm thepatterna 0.4C temperature rise within about ten seconds of the nail being added. More students getinvolved and a range of thermometers is retrieved to repeat the test.

Three mercury thermometers calibrated to 0.2C and two alcohol filled clinical thermometerscalibrated to 0.1C are used to confirm the results in separate experiments. The consistency of theresult from this procedure, regardless of how we measure it, leads us to conclude that the reaction isexothermic. The result is a reliable consequence of what we have done, regardless of how wechoose to measure it (as long as the measuring device is sensitive enough to allow an accuratemeasurement of the temperature change to be made). The term reliability refers to the consistencywith which we can confirm the result (in this case the temperature change).

However, is the above procedure a valid test for the claim that the reaction between a nail and anacid is exothermic? That depends on the certainty we have that the source of heat causing the

temperature change is the result of the reaction between the nail and the acid and not from someother process. The procedure is valid only if the source of heat in the solution causing thetemperature to rise by the amount recorded is the result of a reaction between the nail and acid.

To be sure, you would have to rule out the possibility that the acid was reacting with a protectivecoating on the nail. One procedure to sort that out might be to polish the nail with steel wool beforeputting it in the acid. To rule out the possibility that the nail (or its coating) is a catalyst for a reactionbetween the acid and some unknown contaminant in the acid, is a bit more complex. It would requireyou to both polish the nail and to seek a new source of acid.

The need for accuracy of data should influence the choice of equipment for conducting first-hand

investigations.Where data is collected, quantified or evaluated, reliability refers to the consistency of theinformation; validity refers to whether the measurements you are taking are caused by the

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phenomena you are interested in. The relationship between reliability and validity can be confusingbecause measurements can be reliable without being valid. However, they cannot be valid unlessthey are reliable.

As you can see from the above, it is easier to be confident of your conclusion when there are limitedvariables involved and ones that can be relatively easy to control. You might now begin tounderstand why it was very difficult to establish the link between smoking and lung cancer and thelink between mesothelioma and asbestos dust. How long, if ever, will it take to establish whether

using digital mobile phones causes brain cancer? The more complex the situation in terms ofvariables to control, the less certain we can be that one test will deliver the answer.

Collecting data from secondary sources

When students have to assess the reliability and validity of information and data from secondarysources, the best procedure is to make comparisons between data and claims of a number ofreputable sources, including:

other teachers, science texts and other references, other scientists and information fromreputable sites on the Internet.

In determining validity, students might consider the degree to which evidence supports the assertionor claim being evaluated. In some cases, students may be able to make observations or conductexperiments to confirm the reliability, accuracy and validity of the information they have identified.

Some good questions to ask:

first-hand information and data secondary information and data

reliability Have I tested with repetition? How consistent is the information with informationfrom other reputable sources? If the information wassourced from a web site was it reputable (eg .gov,.org) and was the authors name provided.

validity Does my procedure experimentactually test the hypothesis that Iwant it to? What variables have I

identified and controlled?

How was the information gathered? Do the findingsrelate to the hypothesis or problem?

accuracy The degree of closeness orcorrectness to the true value; %difference to true/data book value

How correct is the information against acceptedunderstanding

science skills stages 4-6(2)

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