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SOC 3811 Basic Social Statistics

SOC 3811 Basic Social Statistics. Announcements. Assignment 2 Revisions (interpretation of measures of central tendency and dispersion) — due next lab. No midterm exam revision policy. . Class overview. Concept review - descriptive v.s. influential statistics

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SOC 3811 Basic Social Statistics

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  1. SOC 3811 Basic Social Statistics

  2. Announcements • Assignment 2 Revisions (interpretation of measures of central tendency and dispersion)—due next lab. • No midterm exam revision policy.

  3. Class overview • Concept review - descriptive v.s. influential statistics - null and alternative hypotheses - test statistics (sampling distributions) - type 1 and type 2 errors • M & M activities

  4. Inferential Statistics • Descriptive statistics: to describe or summarize the data of a sample • Inferential statistics: to make generalizations about a population using a sample eg: GSS —> the American Population (estimators parameters)

  5. Necessary conditions for inference • With a large enough N. • It is representative. • It’s a random sample. (We take it at lots of different times and places.) Usually if the sample is truly random, it will also be representative.

  6. How to make inferences? • Need to do hypothesis testing! • Steps: 1. create your hypotheses 2. random sampling 3. make statistical tests 4. draw the conclusion (reject or accept your hypothesis. )

  7. Test the null hypothesis • Create hypotheses: the null hypothesis and alternative hypothesis should be mutually exclusive. • Get the “estimates” from random samples. • Test if the estimate is a close estimate? (Hint: if the null hypothesis is true, what are the expected behaviors of some test statistics? Compare if these test statistics behave close enough. )

  8. Sampling distributions • Central Limit Theorem

  9. Test statistics • z, t, χsquare, F. • specify α: we can set an acceptable confidence interval (/ probability of type 1 error, usually it’s .05) • Compare the value of the statistic with the expected test statistic.

  10. Type of errors

  11. Examples

  12. M&M Activity • http://us.mms.com/us/about/products/ • Don’t eat your candies before you count them!!

  13. Hypothesis Test: Steps • State research hypothesis • State null hypothesis • Choose a probability of type 1 error. (This tells you how sure you want to be, 90%, 95%, 99%, etc.) • Run an analysis in SPSS. (Determine mean and s.d. and significance level.) • Compare the results to the predetermined values in steps 2 & 3. • Decide whether you will accept or reject the null hypothesis.

  14. Hypotheses? • H0: p = .24 • Ha: p ≠ .24

  15. Test statistic

  16. Conclusion? • for α=.05 (95% confidence level), Z=1.96 (Table D.2 in the textbook) • Our conclusion?

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