15. A normal distribution has a mean of =90 and a standard deviation of =10. For each of the following scores, indicate whether the tail is to the right or left of the scores. And find the proportion of the distribution located in the tail.

A. X=80

B. X=100

C. X=70

16. The following data summarize the results from an independent-measures study comparing three treatment conditions.

1 2 3 n=5 n=5 n=5 M=2 M=5 M=8 N=15 T=10 T=25 T=40 G=75 SS=16 SS=20 SS=24 ZX2=525 a. Calculate the sample variance for each of the three samples.

b. Use an ANOVA with alpha = .05 to determine whether there are any significant differences among the three treatment means.

17. The stimulant Ritalin has been shown to increase attention span and improve academic performance in children with ADHD (Evans et al., 2001). To demonstrate the effectiveness of the drug, a researcher selects a sample of n = 20 children diagnosed with the disorder and measures each child's attention span before and after taking the drug. The data show an average increase of attention span of MD = 4.8 minutes with a variance of s2 = 125 for the sample of difference scores.

a. Is this result sufficient to conclude that Ritalin significantly improves attention span? Use a one tailed test with = .05 to determine whether it is likely that this sample came from a population with D = 0.

b. Use a two tailed test with = .05.

18. In a study examining the effect of alcohol on reaction time, Liguori and Robinson (2001) found that even moderate alcohol consumption significantly slowed response time to an emergency situation in a driving simulation. In a similar study, researchers measured reaction time 30 minutes after participants consumed one 6-ounce glass of wine. Again, they used a standardized driving simulation task for which the regular population averages = 400 msec. The distribution of reaction times is approximately normal with = 40. Assume that the researcher obtained a sample mean of M = 422 for the n = 25 participants in the study.

a. Are the data sufficient to conclude that the alcohol has a significant effect on reaction time? Use a two-tailed test with = .01.

b. Do the data provide evidence that the alcohol significantly increased (slowed) reaction time? Use a one-tailed test with = .01.