PSYC300 Exam 2 Study GuideProfessor BernatBook Chapters: 4,5, and 6- Internal Validity: the experiment tests what it intended to- If an experimental design has internal validity, it means that variation in the dependent variable could only be due to variation in the independent variable- Threats: extraneous variable or confounding variable – a different variable than the independent variable could be causing the variation in the dependent variable- Other threats: o History – something happens between when the first measurement and second measurement are taken that accounts for the variationo Maturation – change in the participants between testso Testing – participants behavior in the second test may change after they have already been tested onceo Instrumentation – instruments used to take the measurements change over timeo Statistical regression – people regress towards the mean over time, i.e. if they score an extreme the first time they are tested, they are more likely to be closer to the average the second time they are testedo Biased selection – the participants in each group of the experiment need to equivalent or it will influence the dependent variable measurementso Experimental mortality – participants drop out- External Validity: the degree to which results generalize beyond your sample and research setting- Threats: highly controlled laboratory setting, restricted populations, pretests, demand characteristics, experimenter bias, subject selection bias- To increase external validity:o Increase sample size so that it is more representative of the entire populationo Decrease experimenter bias (ways to do this are listed on page 4 of the study guide)- Internal validity is more important in basic research, while external validity is more important in applied research- Factors to consider when choosing a measurement:- Reliability: obtain similar results if experiment is repeated- Validity: the measurement measures what you intended it to- To assess reliability:- Test-retest: find the correlation between the score at time 1 and the score at time 2o Best for stable characteristics, but a problem with learning effects- Equivalent Forms: same as test-retest EXCEPT different forms used each timeo Successive measurementso Assume that form A and form B are equal, administer form A the first time and fromB the second time- Split-Half: correlate a person’s score on one half of the items with their score on the other half of the itemso Internal consistencyo If the scale is reliable, correlation between two halves will approach r= 1.00- Interrater: consistency between raterso Measure the difference between rater A and rater B- To assess validity:Construct Validity: the extent to which a measured variable actually measures the conceptual variable it is designed to measure- Subjective Validity:o Face validity: it “looks like” it should work Is the measured variable an adequate measure of the conceptual variable Problems: unscientific, weako Content validity: how well the content of a test measured what it was intended to- Objective validity:o Convergent: the extent to which a measured variable is found to be related to other measured variables designed to measure the same conceptual variableo Divergent: the extent to which a measured variable is found to be unrelated to other measured variables designed to assess different conceptual variablesCriterion Validity: how well a test score can be used to infer an individuals’ performance on some criterion measure:- Predictive Validity: predict future behavioro Ex: if a job aptitude test can predict actual job performance- Concurrent validity: predict current behavioro Ex: if a self- report test can predict an individual’s current moodReliability and Error:- Actual score = True Score + random error- Reliability = true score/ actual scoreo The actual score in their measured score from the testo True score is their actual measurement of the variable in real lifeo Ex: a measure score would be your IQ score, but a true score would be your true IQo You want a measure with as little error as possibleScales of Measurement:- Nominal Scaleo Categories have different names, order does not mattero Reflects qualitative differences (gender, ethnicity)o Can be assigned numbers (male=1, female=2)o Statistical procedures: non-parametric- Ordinal Scaleo Categories have different names and are organized sequentiallyo Can determine differences and direction of the differenceso Cannot say how big the differences areo Statistical procedures: non-parametric- Interval Scaleo Categories organized sequentially, all categories are the same sizeo Has an arbitrary zero point (zero of whatever is being measured does NOT mean an absence of what is being measured), ex: temperature in Celsiuso Can determine the size of the differenceso Statistical procedures: parametric- Ratio Scaleo Equal, ordered categories, with a non-arbitrary zero point (weight, percent correct)o Zero is the complete absence of the variable being measuredo Appropriate statistics: parametricFactors affecting choice of measurement:- Information yielded:o Nominal scale = least informationo Ordinal scale = adds crude informationo Interval & ration scales = most information- Statistical tests available: o Nonparametric tests (used for nominal and ordinal data) are less powerful than parametric tests (used for interval and ration data)o Use scale that allows you to use the most powerful statistical test- Ecological Validity:o Using a measure that reflects what people do in the real world, have scales that have ecological validityo Choose ecological validity even if it means loss of informationDifference between measures:- Categorical: qualitative data, cannot be measured with numbers, i.e. gender, ethnicity- Continuous/Quantitative measures: can be measured numerically, i.e. age, test scoresOverall threats to validity:- Reactivity: the participant changing their answers or behavior because they know they are being observedo Social desirability: natural tendency for research participants to present themselves in a positive or socially acceptable way to the researcho Self-promotion: occurs when research participants respond in ways that they think will make them look goodo Reduce threat of reactivity by: Administering other self report measures that measure the tendency of the participant to lie or self promote Use a cover story- tell the participants that one thing is