2 Validity of Dependent Variables Does it measure the concept?Construct Validity: Does DV really capture what you want to measure (good operational definition?)Or does it include mood, culture or gender bias, confusing wording, observational bias, etc.
3 Indicators of Construct Validity Face Validity: Does it appear to be a good measure (do experts think so?)Predictive Validity: Predict later behavior- GRE=grad school success?Concurrent Validity: Are those known to diverge different in scores (Self Monitoring)
4 Indicators of Construct Validity Convergent Validity: do other kinds of ratings agree? Similar responses to similar scalesDivergent validity: is it different from other constructs? (measures intell, not SES or gender bias) shy isn’t lonlinessReactivity- knowing you are being studied changes behavior
5 Reliability of DV Are results repeatable? All measurement contains true score plus error of measurementNot an issue of replication- same subjects=same scores
6 Types of ReliabilityInter-rater reliability- calculate r for observers or Cohen’s KappaInternal consistency- split half reliability Cronbach’s Alpha calculates ave of all possible corr.Temporal consistency- test-retest reliability with SAME peopleRestaurant example
7 Can a variable be reliable and not valid? Valid and not reliable? How do you know you have a good DV?Mental Measurements Yearbook
10 Internal validityDoes the design test the hypothesis we want it to test? Did IV manipulation cause change in DV? Can we infer causality?What if internal validity is low?
11 External validity Does your study represent a broad population? Caution with Discussion Section if weakRandom SamplingStratified SamplingBlock Randomization
12 Ecological validity Does study reflect the real world- do people really behave this way?Can you study anything without changing it?
13 Threats to Internal Validity: In pre-post design:Test participantsAdminister IVPost test for effect of IVCompare pre vs. post results to look for effect of IV
14 HistoryWorld events may cause change in attitudes or behavior over time.Tests of patriotism pre/post 9/11Views of President pre/post KatrinaAttitudes of adolescents pre/post Cobain suicide
15 Maturation Individuals change over time as they mature. Issue for studies of children, but also huge growth in freshman year- change of attidues and behavior.
16 Testing The study you use may cause differences in behavior. Similar to REACTIVITY, but for entire study not just DV. Parenting study for example
17 Instrumentation Use of instrument may get better or worse with time Observation studiesTesting skill/ interviewing
18 Regression toward the mean Extreme scores do not tend to be repeatable- those who score very high or very low on a test will be closer to the average if tested again.A big issue for any study where pretest is used to select subjects for post test.
19 MortalityThose who drop out of your study may differ from those who choose to continue.
20 Placebo effectIf given any treatment, behavior will change, even if treatment was not meaningful. (fake drugs get some results)
21 How can we improve internal validity? HistoryMaturationTestingInstrumentationRegression toward the meanMortalityPlacebo effect
22 Improved Design In pre-post design: Two Group design Test participantsAdminister IVPost test for effect of IVCompare pre vs. post results to look for effect of IVTwo Group designPretest (do you need to do this?)RANDOMIZED assignment to levels of IVCompare post test results of IV and Control groups
23 Extraneous VariablesAny variable that you have not measured or controlled (RA) that may impact the results of your study
24 Demand Characteristics Participants behave in ways demanded by the situation or experimental set-up. Behavior does not reflect actual beliefs or attitudes.Issue of Ecological Validity
25 Subject Bias Bias brought on by subjects beliefs (Overhead of mood and menstrual cycle)
26 Social desirabilitySubjects want to do the “right thing” and try to guess what the experimenter wants, and do not behave naturally.How to reduce Subject biases?
27 Experimenter BiasExperimenters’ behavior and expectations can sway results of test.How to reduce these biases?
28 Floor & Ceiling Effects If measures are too easy or too difficult you will not see differences between groups.Pilot test with similar subjects!
29 Order effectsWhen using within subjects designs, order of presentation can affect results in several ways. Practice effects: Subjects get better at task with successive trials Fatigue effects: Subjects get tired and do worse or lose interest Carryover effects: subjects experience in one condition impacts results of another condition- subject bias or anchoring and adjustment issues.
30 How to reduce order effects CounterbalancingDoes not get rid of effects, it just makes them equal for all groups. Can do complete counterbalancing if small number of conditions.Latin Square counterbalancingA, B, skip, C, skip, D, etc. then fill backA, B, N, C, N-1, D, N-2, E etc.
31 A Latin Square for 6 conditions Order1ABFCED23456
32 Pretest Vs. Pilot test When do you use a pilot test? When do you use a pre test?