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A school psychologist wishes to determine whether a new antismoking film actually reduces the daily consumption of cigarettes by teenage smokers. The mean daily cigarette consumption is calculated for each of eight teen-age smokers during the month before and the month after the film presentation, with the following results:

When deciding on the form of the alternative hypothesis, H1, remember that a positive difference score (D = X1 €“ X2) reflects a decline in cigarette consumption.)

(a) Using t, test the null hypothesis at the .05 level of significance.

(b) Specify the p - value for this test result.

(c) If appropriate (because the null hypothesis was rejected), construct a 95 percent confidence interval for the true population mean for all difference scores, and use Cohen€™s d to obtain a standardized estimate of the effect size. Interpret these results.

(d) What might be done to improve the design of this experiment?