1. A team of researchers (Singer et al., 2000) used the Survey of Consumer Attitudes to investigate whether incentives would improve the response rates on telephone surveys. A national sample of 735 households was randomly selected, and all 735 of the households were sent an "advance letter" explaining that the household would be contacted shortly for a telephone survey. However, 368 households were randomly assigned to receive a monetary incentive along with the advance letter, and of these 286 responded to the telephone survey. The other 367 households were assigned to receive only the advance letter, and of these 245 responded to the telephone survey.

Set up a two-way contingency table (4 pts)

Calculate and interpret the relative risk (2 pts)

Calculate a confidence interval and interpret it. (4 pts)

Calculate a standardized statistic for these data and hypotheses (3 pts)

Make a decision in regard to the null hypothesis (use either the confidence interval or

the standardized statistic). WHY did you make your decision? (2 pts)

Write conclusion. (2 pts)

1. We discussed the benefits of paired designs in class. Specifically, we talked about the way paired designs affect strength of evidence. Below is the general formula for the standardized statistic. (5 pts)

stat-hyp value /standard error

Mark the value that using a paired design affects.

Does a paired design typically make the value in a) larger or smaller? WHY?

What effect does this have on strength of evidence? WHY?

1. For each of the following situations, mark the appropriate analysis:

a) Ten diamond rings are shown to two jewelers and each jeweler is asked to determine the appraisal value for each ring. The goal is to test whether the two jewelers give the same appraisal values on average.

a. Two independent samples comparison of means

b. A paired comparison of means

c. Regression

b) A sample of 10 faculty members and a sample of 20 students are asked how much time they spent on schoolwork last weekend. The goal is to test whether one group tends to spend more weekend time on average than the other on schoolwork.

a. Two independent samples comparison of means

b. A paired comparison of means

c. Regression

In a study conducted in New Zealand, Parkin et al. randomly assigned volunteers to either wear socks over their shoes (intervention) or wear usual footwear (control) as they walked downhill on an inclined icy path. Researchers standing at the bottom of the inclined path measured the time (in seconds) taken by each participant to walk down the path. 14 persons were assigned to the control group with the sample mean being 37.7 and sample SD being 9.36. 15 persons were assigned to the intervention group with the sample mean being 39.6 and sample SD being 11.57. Note that the data are fairly symmetric in both groups.

Write the null and alternative hypothesis in words and in symbols

Calculate AND interpret a 95% confidence interval to test the hypotheses above

Calculate the standardized statistic.

Does the data provide evidence that people wearing socks over their shoes will take a

shorter time to walk down an icy, steeply inclined road, on average, compared to those

wearing usual footwear? Write decision and conclusion.