Inferring and Explaining

104 InferrIng and exPlaInIng 3. Teaching evaluations for online courses have notoriously low response rates. Less than 10 percent of my online students return their course evaluations. What kinds of bias might infect the accuracy of these student evaluations? Is this sample close enough to practical randomness to tell us anything interesting about the quality of my online teaching? QuIz eleVen A recent Gallup News story claims that “public concern about global warming is evident across all age groups in the U.S., with majorities of younger and older Americans saying they worry about the problem a great deal or fair amount. However, the extent to which Ameri- cans take global warming seriously and worry about it difers markedly by age, with adults under age 35 typically much more engaged with the problem than those 55 and older.” 13 The following results were “based on aggregated telephone interviews from four separate Gallup polls conducted from 2015 through 2018 with a random sample of 4,103 adults, aged 18 and older, living in all 50 U.S. states and the District of Columbia. For results based on the total sample of national adults, the margin of sampling error is ±2 percentage points at the 95% confdence level. All reported margins of sampling error include computed design efects for weighting.” 14 Here is a summary of their fndings: 75 percent of respondents aged eighteen to thirty- four believed that “global warming is caused by human activities,” while only 55 percent of respondents aged ffty-fve and over believed this. Apropos our earlier discussion, 73 percent of the younger cohort thought “most scientists believe global warming is occurring,” but only 58 percent in the older group thought this was true. 15 Based on the information in the Gallup polls, use the techniques developed in this chapter to evaluate the quality of evidence we have for the author’s claim that “the extent to which Americans take global warming seriously and worry about it difers markedly by age.” Here is the complete article from Gallup : https://news.gallup.com/poll/234314/global -warming-age-gap-younger-americans-worried.aspx. Notes 1 Quoted in Sourav S. Bhownick and Boon-Siew Seah, Summarizing Biological Networks (New York: Springer, 2017), vii. 2 Heather Long, “In U.S., Wage Growth Is Being Wiped Out Entirely by Infation,” WashingtonPost , August 10, 2018, https://www.washingtonpost.com/business/ 2018/08/10/america-wage-growth-is-getting-wiped -out-entirely-by-inflation/?noredirect=on&utm _term=.65fd9f744116. 3 Ronald Giere, Explaining Science (Belmont, CA: Wad- sworth, 2005), 142–44. 4 Peverill Squire, “Why the 1936 Literary Digest Poll Failed,” Public Opinion Quarterly 52, no. 1 (Spring 1988): 128. 5 Squire, 128. 6 Audie Cornish, “Do Polls Miss Views of the Young & Mobile?,” NPR, October 1, 200 7, http://www.npr .org/templates/story/story.php?storyId=14863373. 7 Al Gore, An Inconvenient Truth (Emmaus: Rodale, 2006), 262.