4.11STATISTICS IN SUMMARY

Chapter Specifics

imageIn Chapter 3, we saw that random samples can provide a sound basis for drawing conclusions about a population parameter. In this chapter, we learned that even when we take a random sample, our conclusions can be weakened by undercoverage, processing errors, response errors, nonresponse, and wording of questions. We must pay careful attention to every aspect of how we collect data to ensure that the conclusions we make are valid. In some cases, more complex probability samples, such as stratified samples, can help correct nonsampling errors. This chapter provides a list of questions you can ask to help you assess the quality of the results of samples collected by someone else.

CASE STUDY EVALUATED Use what you have learned in this chapter to evaluate the Case Study that opened the chapter. In particular, do the following.

  1. 1. Answer the questions given in the section “Questions to Ask before You Believe a Poll” on page 80.

  2. 2. Are the results of the Pew poll useless? You may want to refer to the discussion on pages 7679.

image Online Resources

  • The video technology manuals explain how to select an SRS using Excel, JMP, Minitab, and the TI 83/84.

  • The Statistical Applet Simple Random Sample can be used to select a simple random sample when the number of labels is 144 or fewer.