1) The mean lifetime of cardiac stents is 8.9 years. A medical device company ha
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Question
1) The mean lifetime of cardiac stents is 8.9 years. A medical device company has implemented some changes to the manufacturing process and wants to determine if these changes affect the mean lifetime. The company performed a study with 40 new devices and found the sample mean lifetime was 9.7 years and the sample standard deviation was 3.4 years. Is there statistically significant evidence, at the 0.05 level, to conclude that the population mean lifetime is different from 8.9 years? To address this question, do the following:Explanation / Answer
e)here std error =std deviation/(n)1/2 =0.5376
hence test stat =(X-mean)/std error =(9.7-8.9)/0.5376=1.488
as critical value of z at 0.05 l;evel =+/-1.96
and test stat is lower then critcal value we cvan not reject that mean is 8.9
f) for 95% CI, z=1.96
hence confidence interval =mean +/- z*std error =8.646 ; 10.754
g) as our confidence interval contains 8.9 as probable value we can not reject that mean is 8.9.
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