For problem 8-50, construct a 95% confidence interval for the difference in stock performance.

In problem "Strategizing for the future" is management lingo for sessions that help managers make better decisions. Managers who deliver the best stock performance get results by bold, rule-breaking strategies. To test the effectiveness of "strategizing for the future," companies' 5-year average stock performance was considered before, and after, consultant-led "strategizing for the future" sessions were held.

Before (%) After (%)

10 ...........12

12 .......... 16

8 ............ –2

–5 .......... 10

–1 .......... 11

5 .......... 18

–3 .......... –8

16 .......... 20

–2 .......... –1

13 .......... 21

17 .......... 24