Refer to Exercise 1132 about the effect of zinc lozenges on

Refer to Exercise 11.32 about the effect of zinc lozenges on the duration of cold symptoms. For  in the zinc lozenge group, the mean overall duration of symptoms was  days, and the standard deviation was  days. For  in the placebo group, the mean overall duration of symptoms was  days and the standard deviation was  days.

Exercise 11.32 Data: Volunteers who had developed a cold within the previous 24 hours were randomized to take either zinc or placebo lozenges every 2 to 3 hours until their cold symptoms were gone ( Prasad et al., 2000). Twenty-five participants took zinc lozenges, and 23 participants took placebo lozenges. The mean overall duration of symptoms for the zinc lozenge group was 4.5 days, and the standard deviation of overall duration of symptoms was 1.6 days. For the placebo group, the mean overall duration of symptoms was 8.1 days, and the standard deviation was 1.8 days.

Calculate   and also compute the unpooled.

Compute a  confidence interval for the difference in mean days of overall symptoms for the placebo and zinc lozenge treatments, and write a sentence interpreting the interval. Use the unpooled standard error and use the smaller of  and  as a conservative estimate of degrees of freedom.

Is the interval computed in part (b) evidence that the population means are different? Explain.

Solution