Computer use. A random sample of 197 twelfth-grade students from across the United States was surveyed, and it was observed that these students spent an average of 23.5 hours on the computer per week, with a standard deviation of 8.7 hours. If we plan to use these data to construct a 99% confidence interval, the margin of error will be approximately (pick only one)

1. 0.07
2. 0.62
3. 1.6
4. 8.7

The meaning of significance. Asked to explain the meaning of "statistically significant at the =0.05 level," a student says: "This means that the probability that the null hypothesis is true is less than 0.05." Is this explanation correct? Why or why not?

How far rich parents take. How much education children get is strongly associated with the wealth and social status of their parents. In social science jargon, this is socioeconomic status (SES). But the SES of parents has little influence on whether children who have graduated from college go on to get more education. One study looked at whether college graduates took the graduate admissions tests for business, law, and other graduate programs. The effects of the parents' SES on taking the LSAT test for law school were "both statistically insignificant and small."

• What does "statistically insignificant mean" mean?
• Why is it important that the effects were small in size as well as insignificant"

Totals aren't enough. Here are the row and column totals for a two-way table with two rows and two columns:

a	b	40
c	d	60
60	40	100

Find two different sets of counts a, b, c, and d for the body of the table that give these same totals. (This shows that the relationship between two variables cannot be obtained from the two individual distributions of the variables because there is not a unique set of counts that gives the sample totals. You also encountered this idea during the exercise on Titanic survival rates and passenger class.)