Research Methods

Chapter 2

Reasoning Fallacies• Hindsight bias – tendency to believe,

after learning an outcome, that we would have foreseen it• The “I knew it all along” phenomenon

Psychology as Science

• Empiricism – belief that accurate knowledge of the world requires observation of it• Limitations of casual

observation:• Unstable• Can’t tell us

about the properties we might be interested in

Psychology as a Science -cont-

• So we must use measurement to:• Define the property we want to

measure in concrete terms• Operational definition – description

of procedures used to define research variables

• Ex: human intelligence may be operationally defined as what an intelligence test measures

Psychology as a Science -cont-

• A good measurement has• Validity – allows one to draw accurate

inferences from it• Replication– produces the same result

whenever it is used to measure the same thing

Case study• Studying a single individual in depth

Naturalistic observation

• Unobtrusively observing people in their natural environment• Avoid demand characteristics – aspects that

cause people to behave as they think an observer wants/expects them to behave

• Limitations:• Some things psychologists want to observe

don’t occur naturally• Some things can only be gathered from

direct observation with a person

Survey• Survey - uses a representative

sample of people to estimate attitudes or reported behaviors of a whole population

• Limitation:• Respondents may not answer

honestly

Survey -cont-• Population - all

the cases in a group being studied from which samples may be drawn

• Random sample - every member of a population has an equal chance of inclusion

Correlational Studies• Correlation – the

“co-relationship” or pattern of co-variation between two variables• Positive – two sets

of variables go up or down together

• Negative – two sets of variables relate inversely

Correlation vs. Causation

• Third-variable correlation – two variables may be correlated only because they are both caused by a third variable• Correlation does

not prove causation

Correlation -cont-• Illusory

correlation: The perception of a relationship where none exists

Experimentation• Used to establish the casual relationship

between variables• Independent variable – variable that is

manipulated• Is “independent” of what the participant says/does

• Dependent variable – variable that is measured• “Depends” on what the participant says or does

• Control group – group that does not receive the treatment

• Experimental group – group does receive the treatment

Experimentation -cont-• An experiment is internally valid when:

• An independent variable has been effectively manipulated

• A dependent variable has been measured in an unbiased way with a valid, powerful, and reliable measure

• A correlation has been observed between the independent and the dependent variable

• External validity – property of an experiment in which the IV and DV is operationally defined in a normal, typical, or realistic way

Experimentation -cont-• It is generally not feasible to use a random

sample when conducting an experiment• Experiments utilize

• Random assignment - assigning participants to experimental and control groups by chance

• Double blind procedure - neither the research participants nor the research staff know if participants received the treatment or a placebo - sugar pill

• Eliminates placebo effect - experimental results caused by expectations alone

Measures of Central Tendency

• Mean – sum of a set of scores in a distribution divided by the number of scores• Extreme scores have a greater impact on the

mean than on the mode or median

• Median – score that divides a frequency distribution exactly in half, so that the same number of scores lie on each side of it

• Mode – the most frequently occurring score in a distribution

Measures of Variation

• Definition – a single score that presents information about the spread of scores in a distribution

• Range – the highest score in a distribution minus the lowest score

• Standard deviation – a standard measurement of how much the scores in a distribution deviate from the mean

• Normal distribution• Form a bell-shaped curve• In a normal distribution of test scores,

50% of scores fall at or above the mean score and 50% of scores fall at or below the mean score

• Approximately 1/3 of the scores fall one standard deviation below the mean and 1/3 fall one standard deviation above the mean

• All score-based normal curves have the following 68-95-99.7 rule in common:• Approximately 68% of all

scores fall within one standard deviation of the mean

• Approximately 95% fall within two standard deviations of the mean

• Approximately 99.7% fall within three standard deviations of the mean

Skewed distributions• Positively skewed distributions have

more scores on the low end of the scale• The median is the best representation

of central tendency

• Negatively skewed distributions have more scores on the high end of the scale• The median is a better representative of

central tendency

Ethics1. Obtain informed consent – written agreement to

participate in a study made by an adult who has been informed of all the risks participation may entail

2. Participation may not be coerced3. Psychologists must protect participants from physical

or psychological harm4. Risk of embarrassment or minor pain must be

outweighed by social benefits of new knowledge gained by study

5. Must provide a debriefing – verbal description of true nature and purpose of study