The document discusses key concepts in statistics including population versus sample, confidence intervals, and how to interpret confidence intervals. It provides examples of confidence intervals and explains that wider intervals indicate less stability while narrower intervals signal more stability. It also gives a three part framework for interpreting confidence intervals that specifies the confidence level, estimated population parameter, and the confidence interval endpoints.

2.  Questions?
 Population and samples: definitions +
differences
 Review confidence intervals
 Practice problems

3.  Population: “all possible measurements or
outcomes that are of interest to us in a
particular study”
 Sample: “portion of the population that is
representative of the population from which
it was selected”
 Representative v. non-representative sampling

4.  
Is the WSPS a population or a sample?

5.  A confidence interval is an interval estimate
of an unknown population parameter, based
upon a random sample
 Interval estimate: range within the
confidence interval.
 Example: [280, 310]
 What is the point estimate for the above?
 Think of confidence intervals as “plausible
values” for a parameter

6.  Plausible estimate of the range
 For 95% CI, you have a 5% chance of
_______________________________
 Will a 99% CI be wider or narrower than a 95% CI?
 Stability of the estimate itself
 Wider confidence interval around the mean – or
proportion – signals relative instability
 Narrow confidence interval signals relative
stability

7. 

8. 

9. Interpretation of confidence intervals should:
1) Clearly state the confidence level (CL)
2) Explain what population parameter is being
estimated (mean or proportion)
3) Should state the confidence interval (both
endpoints).
 "We estimate with ___% confidence that the true
population mean (include context of the problem) is
between ___ and ___ (include appropriate units).“
(Dean and Ilowksy 2012)

10. Assume that a school district has 10,000 6th
graders. In this district, the average weight of a
6th grader is 80 pounds, with a standard
deviation of 20 pounds. Suppose you draw a
random sample of 50 students. What is the
probability that the average weight of a
sampled student will be less than 75 pounds?