On January 29, 2011, visitors to the CNN.com website were invited to answer a poll question. The results are shown below:

Are you exercising more in 2011?

A 99.9% confidence interval for the population proportion (of €œyes€ responses) turns out to be (0.484, 0.495).
a. Explain (using no more than 10 words, preferably no more than 5 words) why this confi dence interval is so narrow.
b. The standardized z-statistic for testing the null hypothesis that 50% of American adults claim to be exercising more in 2011 turns out to be ˆ’6.52, for a p-value of 2.5 × 10ˆ’10. Explain what this indicates about the difference between statistical significance and practical importance.
c. Even if this question could have been asked of every American adult on January 29, 2011, the results would still be questionable. Describe one reason for this.

d. Explain why you think CNN.com adds the disclaimer that €œthis is not a scientific poll.€

Transcribed Image Text:

NO 51% 49,254 YES 49% 47,232 Total votes: 96,486 This is not a scientific poll