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SOC 3811 Basic Social StatisticsPowerPoint Presentation

SOC 3811 Basic Social Statistics

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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

- null and alternative hypotheses

- test statistics (sampling distributions)

- type 1 and type 2 errors

- M & M activities

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)

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.

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. )

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. )

Sampling distributions

- Central Limit Theorem

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.

M&M Activity

- http://us.mms.com/us/about/products/
- Don’t eat your candies before you count them!!

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.

Hypotheses?

- H0: p = .24
- Ha: p ≠ .24

Conclusion?

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

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