note slide 8 lectures : 18/4 + 22/4 + 25/4 + 27/4(first 22

Copyright ©2012 by Pearson Education, Inc.

All rights reserved.

Foundations of Nursing Research, Sixth Edition

Rose Marie Nieswiadomy

Note slide 8

Lectures : 18/4 + 22/4 + 25/4 + 27/4(first 22

min )

Notes written in pink color

Done by ; nursing lijan

FOUNDATIONS OFNURSING RESEARCH

Sixth Edition

CHAPTER





Populations and

Samples

11





Learning Objective One

Define Population And Sample





Population

• Complete set of persons or objects

• Common characteristic

• Of interest to the researcher

مجتمع الدراسة

الباحث مهتم فيه ولاحقا بيطمح لانه يعمم النتائج عليهم

ما بقدر اعمل عليهم الدراسة لانه عددهم كبير

quantitative بيكون حجمه كبير ب

Qualitative بيكون الحجم قليل ب





Sample

• Subset of a population

• Sample represents the population.

عينة الدراسة

لازم تكون ممثلة لمجتمع الدراسة وهي حزء منه





Sample Selection

• Representation of the population

• Method for getting the sample

عشوائية ومنتظمة

• Sample size for the study

Depend if qualitative or quantitative

تعتمد عليها قوة البحث





Sample Terms

• Element (participants )

– Single member of a population

• Sampling frame

– Listing of all elements

– Study sample

باحث بده يعمل بجثه على طلبة الجامعة الاردنية كلية :مثلا

التمريض فبييجي بحط كل الاسماء عورقة وهو بيصير يختار

منهم سواء اختيار عشوائي او حسب مميزات معينة وهيك بتكون

سهلت عالباحث الاختيار





Learning Objective Two

Distinguish Between Target And

Accessible Population





Population Terms

• Target population

• Accessible population





Target Population

• Definition

– Entire group of people or objects

– People or objects meet designated set of

criteria.

– Generalization of the findings





Accessible Population

• Definition

– Group of people or objects

– Researcher has access to them.

بقدر الباحث يوصلهم ومنهم بوخذ العينة تاعت الدراسة





Population Importance

• Conclusions based on data

• Data from accessible population

• Decisions made from study results





Learning Objective Three

Discuss Probability And Nonprobability

Sampling Procedures





Types of Sampling Methods

• Probability

• Nonprobability





Probability Sampling

• Uses random sampling procedures

• Selects sample from elements or members of population

• Types

– Simple

– Stratified

– Cluster

– Systematic

ة الدراسةبتعطي فرصة متساوية لكل شخص بجتمع الدراسة انه يكون ضمن عين•

لك هاد النوع افضل من النوع الثاني لانه قادر على تعميم النتائج لكن مع ذ•

السؤال البحثي هو يلي بحدد





Nonprobability Sampling

• Uses nonrandom sampling procedures

• Selects sample from elements or members of population

• Types

– Convenience

– Snowballing

– Quota

– Purposive

باحث بده يعمل بحث على الاطفال يلي تعرضوا للاساءة فالباحث راح : مثلا

يدور على هاي الفئة من الناس





Learning Objective Four

Compare Four Methods Of Probability

Sampling






• Simple random

• Stratified

• Cluster

• Systematic





Random Selection

• Key word in sample selection

• Every subject has an equal chance.






• Allows researcher to estimate the chance

• Helps with inferential statistics with greater

confidence

• Gives the ability to generalize the findings





Simple Random Sampling

• Type of probability sampling

• Importance of this sampling

– Equal chance of selection

– Independent chance of selection

هاد النوع الاكثر قوة واستخداما لكنه غير سهل

Sample frame احد الطرق للاختيار انه بعد ما نعمل

احط الاوراق يلي بتعبر عن المشاركين واختار منهم عشوائيا -1: انه

بستخدم جدول وبختار مربع معين بحيث يكون كل مربع بيمثل مشارك معين-2





Advantages of


• Little knowledge of population is needed.

• Most unbiased of probability method

• Easy to analyze data and compute errors





Disadvantages of


• Complete listing of population is

necessary.

• It is time consuming to use.

..بالكتاب مهم جدا اقراوه1-11جدول





Steps for Simple Random Sampling

• Identify the accessible population or list of

elements

• Choose the method for getting the sample

• Note how easy it is through this example

– Names of elements on slips of paper

– Papers are placed into a hat.

– Individual draws a slip of paper.

– Individual continues until sample number is

met.





Stratified Random Sampling


• Population is divided into subgroups or

strata.

• Simple random sample taken from each

strata





Approaches for


• Proportional stratified sampling

– Determine sampling fraction for each stratum

– Ensure that this stratum is equal

– Proportion in total population

• Disproportional stratified sampling

– Determine stratum is represented

– Used when strata are very unequal

– Note the key word disproportional





Advantages of Stratified

Random Sampling (cont’d)

• Increases probability of being

representative

• Ensures adequate number of cases for

strata





Disadvantages of


• Requires accurate knowledge of

population

• May be costly to prepare stratified lists

• Statistics are more complicated.





Cluster Random Stratified Sampling

• Large groups or clusters, not people, are

selected from population.

• Simple, stratified or systematic random

sampling may be used during each phase

of sampling.





Cluster Random Stratified Sampling

• Cluster sampling is accomplished by dividing the

population into groups -- usually geographically. These

groups are called clusters or blocks. The clusters are

randomly selected, and each element in the selected

clusters are used.

• Stratified sampling also divides the population into

groups called strata. However, this time it is by some

characteristic, not geographically. For instance, the

population might be separated into males and females. A

sample is taken from each of these strata using either

random, systematic, or convenience sampling.





Advantages of

Cluster Random Sampling

• Saves time and money

• Arrangements made with small number

sampling units

• Characteristics of clusters or population

can be estimated.





Disadvantages of

Cluster Random Sampling

• Causes a larger sampling error

• Uses a more complicated statistic analysis





Systematic Random Sampling


• Every kth element is selected.

• Process

– Obtain a listing of population

– Determine the sample size

– Determine the sampling interval (k = N/n)

– Select random starting point

– Select every kth element

الاختيار بيكون كل فترات منتظمة مثلا كل رابع شخص

لانها جدا مهمة K لازم نحدد ال

N= total population

N= sample size





Ex : if population =1000 and sample size = 100

K=10

يلي بالقائمة 10يعني بختار كل عاشر شخص ولازم اول شخص اختاره يكون رقمه من اول

لانه لازم نختار 12فراح يكون رقم الشخص الثاني رقمه 2يعني لو كان رقم الشخص الاول

كل عاشر شخص





Advantages of


• Easy to draw sample

• Economical

• Time-saving technique

biase في شرطين مهمين لازم يتحققوا عشان ما يصير

1- population list

2-k





Disadvantages of


• Samples may be biased.

• After first sample is chosen, no longer

equal chance

ي اول شخص هو يلي بنطبق عليهم الاختيار العشوائي بس الباقk لا لانه راح تنطبق عليهم ال





Learning Objective Five

Compare Methods Of Nonprobability

Sampling






• Sample elements are chosen

nonrandomly.

• Produces biased sample

• Each element of the population may not

be included in the sample.(no equal

chance )

• Restricts generalizations made about

study findings






• Convenience

• Snowballing

• Quota

• Purposive





Convenience Sampling

• Chooses the most readily available subject or

object

• Does not guarantee that the subject or object is

typical of the population

بختارهم بالصدفة

سهلة وسريعة

ية باحث بده يوزع استبيان على طلبة كلية التمريض فراح عالكل: مثال

شخص اخذهم 20واول

المشكلة انه ممكن يلي اختارهم ممكن ما تكون ممثلة لمجتمع البحث





Snowball Sampling

• Type of convenience sampling method

• Study subjects recruit other potential

subjects.

• May be called network sampling

• May find people reluctant to volunteer

انه باخذ مشارك وبحكيله اذا بعرف ناس اخرين عندهم نفس

التجربة وهو بيصير يدلنا عليهم

عدد المشاركين بكبر تدريجيا





Quota Sampling

• Type of nonprobability sampling

• Researcher selects sample to reflect

characteristics.

• Similar to stratified but stratified use

random sample selection but quota use

convenous selection

• قسمنا المشاركين حسب الجنس وبعدها اخترنا اول : مثال quota امراة هاد هو 20





Quota Sampling

• Age

• Gender

• Educational background

• Number of elements in each stratum

• Number is in proportion to size of total

population.





Purposive Sampling

• Type of nonprobability sampling

• Researcher uses personal judgment in

subject selection.

• Each subject chosen is considered

representative of population.

• Many qualitative studies use this

technique.






Procedures

• Advantages

– Time

– Money

• Disadvantages

– Nonrandom

– Not able to generalize findings





Learning Objective Six

Determine Which Sampling Technique To

Use In Various Types Of Research Studies





Research Studies

• Use voluntary subjects

• Follow the ethics of research

– Subjects must voluntarily agree.

– Subjects may refuse to participate

ممكن يكون المشارك شارك بالبحث مش لاعطاء المعلومة وانما

.لهدية او مكافاة





Research Data

• Based on voluntary responses from

subjects

• Biased sample occurs if subjects do not

participate.





Volunteers As Subjects

• Sample selection varies.

– Subjects volunteer for a study.

– Researcher approaches subjects.





Random Sampling or

Random Assignment

• Random sampling

– Each subject has equal probability of being

included.

• Random assignment

– Procedure to ensure that each subject has

equal chance





Threefold Randomization Process

• Used for experimental studies

• Helps represent the ideal study procedure

• Steps to ensure the process

– Subjects randomly selected from population

– Subjects randomly assigned to groups

– Experimental treatments randomly assigned

to groups





Learning Objective Seven

Compare Longitudinal And Cross-Sectional

Studies





Classification of Research Studies

• Longitudinal

بشوف نفس المشاركبين على فترات

• Cross-sectional

بشوف كل المشاركين بوقت واحد





Longitudinal Research Study

• Subjects are followed over time.

• A cohort study is one example.

مجموعة اشخاص بينهم اشي متشابه

• Subjects are studied based on

– Similar age group

– Similar background





Longitudinal Research Study

(cont’d)

• Data are gathered.

– Same subjects

– Several times

– Tells influence of time





Cross-Sectional Study

• Subjects checked at one point in time

• Data collected from groups of people

• Data may represent differences in

– Ages

– Time periods

– Developmental states

– Important considerations





Longitudinal Versus

Cross-Sectional Studies

• Longitudinal studies

– Accurate means of studying changes over

time

– Studies take a long time to perform.

• Cross-sectional studies

– Less expensive

– Take less time

– Easier to conduct





Learning Objective Eight

Enumerate Factors To Be Considered In

Deciding The Size Of The Sample





Sample Size• No simple rules

• Qualitative studies use much smaller samples than

quantitative studies.

• Factors to consider for sample sizes in quantitative

studies

– Homogeneity of population

Homogenous need less sample size than heterogenous

– Degree of precision desired by the researcher

كل ما زادت الدقة كل ما احتاجت عينة اكبر

– Type of sampling procedure that is used

Non probability need small sample size

Probability need large sample size





Sample Size (cont’d)

• Central limit theorem

• Sampling distribution of the mean





Larger Sample Sizes

• Many uncontrolled variables are present.ex; age ,

gender

• Small differences are expected in members.

مثلا لو بدي اربط بين الحمية الغذائية يلي اعطيتها للمشاركين مع نزولهم للوزن

ولاحظنا انه فئة من المشاركين نزلت وزن اكثر وطلع السبب لانهم بمارسوا رياضة معينة

• Population must be divided into subgroups.

• Dropout rate among subjects is expected to be high.

• Statistical tests are used that require a minimum sample

size.





Power Analysis

• Helps to determine sample size

• May prevent type II error

• Helps to detect statistical significance

:العوامل المؤثرة

1-if power analysis is low that increase type 2 error

2- power analysis increase with increase sample

size

3-alpha level





Power Analysis (cont’d)

• External funding sources require it.

• Helps determine the optimum sample size





Nursing Research Studies

• Usually limited to small convenience

samples

• Generalizations to total population difficult

• Small sample sizes warrant replication

studies.

• Similar results from replication help with

generalization.





Learning Objective Nine

Discuss Sampling Error And

Sampling Bias





Sampling Bias

• Bias when samples are not carefully selected

• All nonprobability sampling methods have it.

• May occur in probability sampling methods

– Subjects decide not to participate when chosen.

– Final sample is now not representative of population.

سببه الباحث نفسه

Non probability بتكون اعلى ب

في حال انه المشاركين في منهم ما رد Probability ممكن تصير ب





Sampling Error

• Random fluctuations in data

• Not under the control of the researcher

• Chance variations occur when sample is

chosen.

سببه مش الباحث وانما بالصدفة حدث

نة عن نستدل عليه بانه بيكون في فرق واضح بالافريج تاع العي

الافريج تاع مجتمع الدراسة

..في مثال بالصفحة القادمة





Avg of population = 71

Avg of samples = 63 – 83 – 71

هون الافريج تاع العينات اشي اكبر من افريج المجتمع واشي اصغر

واشي يساوي





Learning Objective Ten

Critique The Sampling Procedure

Described In Research Reports

And Articles





Critiquing the

Population and Samples

• Is the target population identified?

• Is the accessible population identified?

• Was a probability or nonprobability

sampling method used?

• Is the specific sampling method named?

• Is the sampling method described?

• Is the sampling method appropriate for the

study?





Critiquing the Population and

Samples (cont’d)

• Are the demographic characteristics of the

sample presented?

• Is the sample size adequate?

• Was power analysis used to determine the

sample size?

• Is the sample representative of the

population?





Critiquing the Population and

Samples (cont’d)

• Are potential sampling biases identified?

• Is subject dropout discussed?

note slide 8 lectures : 18/4 + 22/4 + 25/4 + 27/4(first 22

Documents