Recently, two political scientists wrote an essay in the New York Times explaining some polling data they had collected on the Tea Party political group in the United States.  

Here's one of the claims in their article: 

"Tea Party supporters have slipped to 20 percent, while their opponents have more than doubled, to 40 percent."

a.  What kind of claim are the authors making here?  What questions should you ask to interrogate it?

Here's another set of statements from their article:  

"Beginning in 2006 we interviewed a representative sample of 3,000 Americans as part of our continuing research into national political attitudes, and we returned to interview many of the same people again this summer. ..

b. What does the phrase "representative sample" mean here?  Is a sample of 3,000 Americans large enough to make a sample representative?  

 

And finally, here's one more set of statements to consider: 

"We can also account for multiple influences simultaneously — isolating the impact of one factor while holding others constant….

"…Actually, the Tea Party’s supporters today were highly partisan Republicans long before the Tea Party was born, and were more likely than others to have contacted government officials. In fact, past Republican affiliation is the single strongest predictor of Tea Party support today."

c. In the first part of the quote above, what does it mean when the authors state that they can isolate one factor while holding others constant?  What kind of analysis does this suggest that the scientists did?

d. In the second part of the quote above, notice that they use the phrase "single strongest predictor."  Using what you learned in Chapter 8, can you imagine what the regression table might have looked like?   (List what the dependent variable was, and what some of the independent variables were, given your reading of the article, and suggest how the results might have supported the claim above.)

 

Suggested answers:

a.  As a frequency claim (about the level of support for the Tea Party among Americans) you should focus on external validity and construct validity in your questioning.  

b. A representative sample is one that was drawn using a random sampling technique.  Because the sample is representative, a sample of 3000 is large enough–it's how the sample is drawn, not how many are in it, that matters for external validity.

c.  This means that the authors probably used a multiple regression technique (see Chapter 8).

d.  We'd have to get more detail on the statistics to be sure.  However, according to this essay, the dependent variable is support for the Tea Party.  The independent variables seem to have included past Republican affiliation, support for religion in the government, suffering economic hardship in the past four years, being white, support for immigrants, and support for abortion, among others.  The statement in question probably means that the beta for Republican affiliation was the strongest one  (Later statements in this essay–those in the 10th paragraph–seem to indicate that support for religion in the government is the second strongest beta in the regression table.)