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Chapter 5
- 1. Measuring Variables andSampling
- 2. Roadmap Today: Begin Exam 2 material (Chapters 5, 6, 4) Scales of measurement Psychometric properties Reliability Validity Tuesday: Finish chapter 5 Discuss Exam 1
- 3. Zoom out: whereare we? We have: A research question An idea for a research design A hypothesis But how do we measure what we’re interested in?
- 4. Scales of Measurement to measure them We study variables and need accurately 4 scales of measurement Nominal Ordinal Interval Ratio
- 5. Nominal Scale symbols classify or categorize into GROUPS or TYPES Name, Categorize, Classify Caution: use of numbers to indicate group Examples- gender, marital status, experimental condition
- 6. Ordinal Scale A rank order scale of measurement Examples- order of finish, Letter grade in class, social class (low, med., high) Allows you to determine which person is higher or lower but not how much higher or lower. Can’t make direct comparisons
- 7. Interval Scale Rank ordering PLUS equal intervals of distance between adjacent numbers Example- Celsius and Fahrenheit temperature, IQ scores, year Now you can make comparisons Equal distances but no absolute zero point
- 8. Ratio Scale rank ordering, equal intervals PLUS an absolute zero point Absolute zero = absence of variable Examples- Kelvin temperature, income, weight, height, response time.
- 9. Psychometric properties Reliability: Consistency/stability of scores Validity: Are you measuring what you are trying to measure? Ideally, we want: Measures that are reliable Inferences that are valid Reliability is necessary but not sufficient in order to have validity
- 10. Think about aTarget
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- 14. Measuring Reliability 4 Primary types Test-Retest Reliability Equivalent- Forms Reliability Internal Consistency Reliability Interrater Reliability Indicate level of reliability with a reliability coefficient Correlation; should be positive and strong (> .70)
- 15. Test- Retest Refers to consistency over time Same measure administered twice (with a time interval between)
- 16. Equivalent-Forms Reliability Equivalent forms- two versions of the same measure Administer to the same group of people Problem- hard to develop equivalent measures Example: SAT, GRE
- 17. Internal Consistency Consistency with which test items measure a single construct. More items increases reliability, but we use as few items as possible Why?
- 18. Example: Internal Consistency I feel sad I feel down I feel depressed I feel miserable I feel awful
- 19. Example: Internal Consistency I feel hungry I feel happy I have green eyes Big Bird is scary I like turtles http://www.youtube.com/watch?v=CMNry4PE93Y
- 20. Internal Consistency Measured using coefficient alpha (α) a.k.a. Cronbach’s alpha Should be .7 or higher High values mean the items are measuring the same construct If your scale measures more than 1 thing, each construct gets its own coefficient α
- 21. Interrater Reliability of ratings made Interrater reliability- consistency by different judges GRE writing section Expressive writing studies Correlation between ratings should be strong/positive
- 22. Interobserver Agreement observers agree percentage of times different % of times raters agree- easy to calculate and understand
- 23. Validity Accuracy of inferences or interpretations made on the basis of scores Measuring schizophrenia, or love We can’t directly observe it! It’s the accuracy of the interpretation from the test
- 24. Validity Construct Operationalization Important to consider: Does your operationalization truly reflect what you’re measuring? Validation Never-ending process
- 25. Obtaining Validity: Based on Content Content validity: judgment of the degree to which items adequately represent a construct’s domain. Do items appear to represent the thing you’re trying to measure? (face validity) Does your measure exclude any important parts of what you’re trying to measure? Does your test measure something besides what you wanted? (i.e., include irrelevant items)
- 26. Obtaining Validity: Based on Internal Structure Some constructs are multidimensional and need measures that address all dimensions Homogeneity—degree to which a set of items measure a single construct Item-to-total correlation Coefficient alpha
- 27. Obtaining Validity: Basedon Relations to Other Variables Criterion-related validity: degree to which scores predict or relate to an already established test Two types of criterion validity: Predictive: using your measure to predict future performance Concurrent: using your measure to predict current performance on the same construct, or a related one.
- 28. Obtaining Validity: Basedon Relations to Other Variables Convergent validity: relationship between your measure and other measures of that same construct Discriminant validity: evidence that scores from your measure are NOT similar to scores of tests on different constructs.
- 29. Appropriate Use ofReliability and Validity Info Reliability and validity info apply to the measure of interest in the reported sample Situation-specific, not broad Standardized tests: norming group If you want to use a test with a group not represented in the norming group, be cautious Report R & V for your own sample, and be wary of articles that make blanket statements about a measure’s R & V