1. PS 366

2. Levels of Measurement How we classify / observe things Affects how they are described Affects what statistics we use to test hypotheses about relationships between things

3. Levels of Measurement Nominal – Things classified or categorized – No rank order – No scale Race, gender, hair color,

4. Levels of Measurement Ordinal – Things classified, categorized – Things ordered, ranked – No set distance between categories – More of, less than Satisfaction with democracy; prejudice; academic rank; party identification

5. Levels of Measurement Interval / ratio – Things measured on a continuous scale – Equal distance between units on scale – (if ratio) zero means zero Age (years); GPA; income; education (years) IQ; Celsius scale[zero = ??]

6. Levels of Measurement Some things (variables) can be measured at each level Example, Pain – Nominal – Ordinal – Numeric (interval)

7. Levels of Measurement Some things not clear cut – Poverty – Freedom – Unemployment – Alienation

8. Levels of Measurement Exercise: Create measures of Education (how much) – Nominal – Ordinal – Numeric (interval) – As a question that can be asked on a survey Exercise: Create measures of Happiness (how much) – Nominal – Ordinal – Numeric – As a question that can be asked on a survey

9. Levels of Measurement Why it matters? – If nominal, ordinal, interval: – How do we describe Central tendency? Variation? What graphics?

10. Nominal Data Simple percentages, proportions – Yes 45%, No 55% Most frequent occurrence (Mode) What is the meaning of the mean of gender? – 200 observations: M = 1, F = 2; mean = 1.5 ?

11. Example: General Social Survey Sex before marriage ok? permarsx Frequency distribution – Analyze -> Descriptive Stats ->frequency – GSS Sex before marriage 1) always wrong, 2) almost always wrong, 3) sometimes wrong, 4) not at all wrong

12. Ordinal data frequency distribution

13. Ordinal Data How describe graphically? Bar charts (categories, but not range of variation)

14. Frequency of responses

15. Ordinal Data – Very satisfied (1)12 – Satisfied (2)15 – Neither satisfied nor dissatisfied (3) 5 – Dissatisfied (4) 5 – Very dissatisfied (5) 3 total40

16. Ordinal data Does it ‘behave’ like interval? Center: Mode

17. Interval Data Mean, median, mode – What is most representative observation Frequency distributions can be ‘normal’

18. Example: General Social Survey Analyze -> descriptives -> frequency – Range 18 – 89 plus: – What’s the distribution going to look like?

19. This is where Powerpoint crashed

20. Interval Data Standard deviation – how is what we observe distributed around the central point Frequency distributions

21. Measuring Concepts But what is a variable? Something that varies – Influences something else; influenced by something else Not a constant – Does not vary [Death, gravity, speed of light ]

22. Measuring Concepts Measuring a variable = Quantifying a concept – turning a concept into something we can measure Nominal, ordinal, interval

23. Measuring Concepts Variable = religion Type? Frequency? Intensity?

24. Measuring Concepts Religion: – Type: Catholic, Baptist, None, Christian [self- identified] – Frequency: How often attend religious services – Intensity: Is Bible literally word of God? Do you believe Jesus is / is not son of God?

25. Measuring Concepts Religion: – Type: nominal – Frequency: Ordinal – Intensity: Interval??? [religiosity?]

26. Measuring Concepts Candidate support – Vote intention – Reported vote – “Feelings” [interval, intensity?]

27. Measuring Concepts Candidate support – Thermometer scores Romney50.4 (23%) Pawlenty48.4 (67) Huntsman47.9 (84) Paul46.3 (34) Bachman45.6 (55) Santorum43.9 (63) Newt42.7 (17) value in parentheses = % unable to rank On a scale of 0-100, with 0 being cold, 50 being neutral, and 100 being warm, how would you rate your feelings rate the following candidates June 15, 2012

28. Reliability and Validity Reliability – Does the method of measuring produce the same results when used by others – Consider religion measures Response to questions: – what is your religion? __________________ – how religious are you? _________________ vs: – Check the label that applies to you [P, C, J, etc. ] – Closed response options [very, sort of, not, not at all]

29. Reliability and Validity Reliability – Does the method of measuring produce the same results when used by others – Consider Intelligence Subjective judgment Written narrative IQ test

30. Reliability and Validity Validity – Construct Validity: does the measure really measure the concept? [Religion & faith] – Predictive Validity: does the measure predict what it should? [PID & voting] – Content Validity: does the measure include things closely related to the concept?

31. Reliability and Validity Validity – Face Validity: Does the measure correlate well with things related to the concept?

32. Reliability and Validity Validity – IQ test measure; SAT score, GRE score What do they really measure? What do they predict? What should they predict if valid measures of ______

33. Reliability and Validity Validity? – Party Identification Strong D D Ind, leans D Ind Ind, leans R R Strong R