1. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. Gathering Useful Data Chapter 3

2. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. 2 The Fundamental Rule for Using Data for Inference Available data can be used to make inferences about a much larger group if the data can be considered to be representative with regard to the question(s) of interest.

3. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. 3 Some key words: observational studies vs. experiments Randomized experiment confounding vs. lurking variable control group, placebo, blinding matched pairs and blocking case-control study prospective vs. retrospective Hawthorne effect…

4. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. Sampling: Surveys and How to Ask Questions Chapter 4

5. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. 5 We talked about: conservative margin of error how to randomize simple random sampling

6. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. 6 The Margin of Error The sample proportion and the population proportion with a certain trait or opinion differ by less than the margin of error in at least 95% of all random samples. Conservative margin of error: For proportions: For percents: Add and subtract margin of error to create an approximate 95% confidence interval.

7. Copyright ©2006 Brooks/Cole, a division of Thomson Learning, Inc. 7 Example 4.1 The Importance of Religion for Adult Americans Poll of n = 1003 adult Americans: “How important would you say religion is in your own life?” Very important65% Fairly important23% Not very important12% No opinion0% Conservative margin of error is 3%: Approx. 95% confidence interval for the percent of all adult Americans who say religion is very important: 65%  3% or 62% to 68%