Psych 317 #2

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Sampling

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How we choose who participates in ourstudy

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Types of sampling

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probability and nonprobability

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probability sampling

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Means that you can explain the likelihood(percentage) that any individual has for becoming a participant.

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Random sample

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•everyindividual in the population has an equal chance of being selected

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Why random samples are not always possible

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–Costly–Timeconsuming–Difficult

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representative sample

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is a sample that includes individuals/participantsrepresentative of a larger population

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Advantages of representative samples

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–“Represents”the larger population–Lookslike the population, only smaller–Shouldbe able to accurately make conclusions and apply it to other samples

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•Disadvantages of representatives sample

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–Createssamplingerror–Needto keep in mind margin of error

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sampling error

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error in a statistical analysis arising from the unrepresentativeness of the sample taken.

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margin of error

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an amount (usually small) that is allowed for in case of miscalculation or change of circumstances.

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SimpleRandom Sampling

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•Everypossible sample (from the total population) has the same chance of beingselected

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sampling frame

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listof all possible participants in a population

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SystematicSampling

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•Choosingevery nth person from a sample

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Problem with systematic sampling

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• notevery person in the sample has equal likelihood of becoming a participant

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StratifiedRandom Sampling

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•Dividethe population into stratabefore conducting simple random sampling

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ClusterSampling

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•Beforechoosing participants, you choose groupings of individuals–Geographically–Byinstitutions

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•a multi-stagecluster samplingmethod

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–Randomlychoose state–Randomlychoose counties–Randomlychoose schools–Randomlychoose participants

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•Most psychology (and other sciences) use this type of sampling

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Nonprobabiltiy sampling

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Nonprobabiltiy sampling

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is a sampling technique where the samples are gathered in a process that does not give all the individuals in the population equal chances of being selected.

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ConvenienceSampling

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sample made up of people who are easy to reach.

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QuotaSampling

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•Conveniencesample that ensures certain types of people are included in the study

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PurposiveSampling

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•Usingpast research to tell you who to sample

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Problemswith Sampling

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•Whochooses to respond•Whatyou are asking about•Individualdifferences •Amountof compensation

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BasicEthical Guidelines

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Must do one of the following:–Addto our basic knowledge –Improvea procedure–Improvea program –Improvequality of life

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Thingsresearchers must do

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–Provideinformed consent• –MinimizeHarm–Debriefparticipants

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Informed consent

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Ensure confidentiality/anonymity •Ensure knowledge that participation is voluntary

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Minimizing Harm

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Therisk of harm must be no greater than in ordinary life.

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DECEPTION

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•Onlyused when knowing ahead of time might influence participants’ responses••Deceptioncannot cause undue stress••Participantsmust be fully debriefed afterwards

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Debriefing

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•Askopen-ended questions •Providea contact so participants can follow-up with additional questions if needed•Funneleddebriefing is best

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Funnel debriefing

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when you start with the most abstract and open-ended questions and then funnel down to the most specific and closed-ended questions

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IRB(and Scientific) Violations

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Fabrication, Falsification, Plagiarism, Ethicalstandards, Suppressingdata

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Fabrication

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making up data

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Falsification

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•manipulatingphysical aspects to get the results you want

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Plagiarism

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•usinganother person’s ideas, processes, results, or words without giving credit

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Suppressingdata

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•ignoringresults because it won’t be “popular”

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DescriptiveResearch

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•Goalis to describe behavior and/or characteristics of a population••Althoughit helps describe what people think or do, it doesn’t explain why•Importantto psychologists because it can help lead to questions that need answered

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Types of descriptive research

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–Survey–Demographic–Epidemiological

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SurveyResearch

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Use questionnaires, interviews orobservational methods to ask participants questions, Importantly survey does not meanquestionnaire!

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Cross-Sectional Survey Design

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•Singlegroup that is supposed to represent thepopulation••One-shotdeal

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Successive Independent SamplesSurvey Design

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•Twoor more different samples complete the same survey at different time points••Importantly,they are different individuals at point 1 and 2

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Longitudinal Survey Design

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Surveying (the same) participants morethan once

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Attrition

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whenparticipants drop out of the study over time

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DemographicResearch

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•Describesbasic life events of a particular sample/population

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EpidemiologicalResearch

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•Studyof disease and death (including mental disorders)•Canhelp psychologists learn if there are certain social groups more or less atrisk

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Measuresof central tendency

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Mean, Median, mode

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Measuresof variability

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–Range–Variance–Standarddeviation

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Nominal scales

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Answers to questions that correspond tobehaviors or characteristics

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Interval Scales

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•Tellsus the rank order or responses and thedifference in-between each value•Notrue zero value ••Zerodoes not mean the absence of something EX. TEMPERATURE

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RatioScales

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•Includeseverything –Meaningfuldistance between numbers–Truezero point–Zeromeans absence of–Numberscorrespond to numbers and not labels EX. WEIGHT

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Fourmain causes of error variance

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1.Individualdifferences (stable attributes)2.Situationalfactors

3Characteristicsof the measure

4 mistakes

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Reliability

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•SystematicVariance divided by

Total Variance

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Test-retestreliability

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>.7

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InteritemReliability

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•Usedwhen we have multiple questions to help us measure a behavior or characteristic••Helpsus understand if the items are consistent with each other AND how they work asa group–Meansthat items need to be .3 or higher with the other items

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Cronbach's Alpha

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>.7

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Face Validity

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•Onthe surface, it looks like we are measuring what we want to

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convergent validity

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Shouldhave high correlation with other measures that are similar

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discriminant validity

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Shouldhave low correlation with items that are different

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Criterion-RelatedValidity

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•Tellsus whether we can predict a behavioral outcome from a measure