A researcher surveyed two groups of Americans about their fears of terrorism-one group in 2005 and the other group in 2015. This is an example of a _______ design.

In a normal distribution, approximately what percentage of scores falls between one standard deviation below the mean and one standard deviation above the mean?

IQ scores are normally distributed, with a mean of 100 and a standard deviation of 15. Approximately what percentage of people have IQ scores that fall below 70?

A researcher used a measure of self-esteem that has a mean of 50 and a standard deviation of 10. If 1,000 respondents completed the scale, how many would she expect to score above the mean?

Scores on a test range from 12 to 90, with a mean of 60 and a standard deviation of 10. If a particular participant scored 40 on the test, his z-score would be