Question

1. We wish to compare list prices of six popular drugs for HIV infection. The data in the table represent means and standard deviations of prices for each drug based on a survey of 55 pharmacies in the New England area. Prices are for a full course of treatment.

1. Generate a graphical display of the mean prices shown in the following table.

Mean and Standard Deviation of Prices of Six HIV Drugs

Drug	Mean Price	Standard Deviation in Price
A	$3,200	$856
B	$6,800	$925
C	$11,352	$754
D	$3,945	$920
E	$2,120	$645
F	$4,856	$540

2. Consider again the data shown in Table above. Compute 95% confidence intervals for the mean price of each drug using x□ ± t ^s . Generate a graphical display showing the means

√n

and 95% confidence intervals for the mean drug prices for each drug group. Based on your calculated estimates, which of the drugs have statistically significantly different prices?

Answer 1

a)

Following is the bar graph of price for 6 drugs -

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b)

As there are 55 pharmacies sampled, so the critical t-statistic for 95% confidence interval is : t_54,0.025 = 2.005.

Thus, the required confidence interval would be -

Thus, we get following table-

Drug	Mean Price	Standard Deviation in Price	Lower Limit	Upper Limit
A	3200	856	2968.58	3431.42
B	6800	925	6549.92	7050.08
C	11352	754	11148.15	11555.85
D	3945	920	3696.27	4193.73
E	2120	645	1945.62	2294.38
F	4856	540	4710.01	5001.99

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And the required graph is as shown -

Note from the error bars that none of the confidence intervals region coincide even a little. Which means that they all have means significantly different from each other.