1. A random sample is collected of size n from a population with standard deviation and with the data collected a 95% confidence interval is computed for the mean of the population. Which of the following would produce a new confidence interval with smaller width (smaller margin of error) based on these same data?
A. Increase .
B. Use a smaller confidence level.
C. Use a smaller sample size.
2. A random sample of 85 students in Chicago city high schools take a course designed to improve SAT scores. Based on these students, a 90% confidence interval for the mean improvement in SAT scores for all Chicago city high school students is computed as (72.3, 91.4) points. The correct interpretation of this interval is
A. 90% of the students in the sample improved their scores by between 72.3 and 91.4 points.
B. 90% of the students in the population should improve their scores by between 72.3 and 91.4 points.
C. Neither choice is correct.
3. A social psychologist reports that "in our sample, ethnocentrism was significantly higher (P < 0.05) among church attendees than among nonattendees." This means
A. ethnocentrism was at least 5% higher among church attendees than among nonattendees.
B. the observed differences between church attendees and nonattendees account for all but 5% of those sampled. These results are quite meaningful and should be investigated further.
C. if there is actually no difference in ethnocentrism between church attendees and nonattendees, the chance that we would observe a difference as large or larger than we did is less than 5%.