PSY 124 Chapter 5, Week 6 Notes
PSY 124 Chapter 5, Week 6 Notes PSY 124 - 03
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This 4 page Class Notes was uploaded by Layne Franklin on Friday February 26, 2016. The Class Notes belongs to PSY 124 - 03 at University of Indianapolis taught by Jordan Sparks Waldron in Fall 2015. Since its upload, it has received 19 views. For similar materials see Fndtns/Psyc Science I:Methods in Psychlogy at University of Indianapolis.
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Date Created: 02/26/16
Chapter 5: Selecting Research Participants Population Entire set of people in which researcher is interested Sample The subset of the population we collect data from Sampling The process by which a researcher selects participants for a study Types of Samples Probability Sample Likelihood that any particular individual in the population will be selected for the sample can be specified Nonprobability Sample No method of knowing probability that a case will be chosen Part I: Probability Samples When do we want them? When we want to estimate proportion of people in a population with certain issues In other words: we need a “Representative Sample” A sample from which we can draw accurate, unbiased estimates of the characteristics of the population of interest External validity: extent to which results of a study generalize to larger population Errors of Estimation Sampling Error Population vs. sample characteristics Entire school vs. 200 students at that school Error of Estimation (Margin of Error) Degree to which the sample data are expected to deviate from the population Function of three things Sample Size Population Size Variance of the Data Simple Random Sampling Simple Random Sample Every possible sample of the desired size has the same chance of being selected from the population Sampling Frame A list of the population from which the sample is to be drawn Have to know how many individuals are in the population, sampling frame has to list all of them Selecting Random Samples Table of Random Numbers Computer Programs Random Digit Dialing Stratified Random Sampling Stratified Random Sampling Population is divided into subgroups (strata) Randomly selected from each subgroup Stratum Subset of the population sharing a particular characteristic Gender, Race, Location Still need a sampling frame Proportionate Sampling Method Cases are selected from each stratum in proportion to their prevalence in the population Systematic Sampling Involves taking every ‘Xth’ individuals for the sample Do not need Sampling Frame at start of study Not a simple random sample Not everyone has an equal chance of being selected for the study Cluster Sampling Sample groupings/clusters of participants Clusters are based on naturally occurring groups Usually in close proximity All psychology majors in Indiana Randomly select 10 colleges/universities in Indiana List of psychology majors from these schools Randomly select students from the lists Advantages Sampling frame of every individual in the population not needed to begin (All we need is a list of clusters) Less expensive, less effort, because: Multistage Cluster Sampling Divide population into large clusters & randomly sample clusters Randomly sample smaller clusters within those large clusters If needed, sample again from those clusters Continue until the appropriate number of participants is chosen Counties → Schools → Classrooms → Students Nonresponse Problem Failure to obtain responses from individuals that researchers select for the sample Why is Nonresponse a Problem? Participants in the study may be systematically different from non- responders Threatens representativeness Preventing Nonresponse Be persistent in contacting participants Offer incentives for participation Limit the amount of time required Tell people in advance that they will be contacted about participation Misgeneralization Generalizing the results of a study to a population that differs from the one from which the sample was drawn Literary Digest Example 2 Million voters surveyed via telephone about 1936 Election Predicted that Alfred Landon would beat Franklin Roosevelt by 15% points. Roosevelt was elected with 62% of popular vote.
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