drbin
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A new treatment for elevated cholesterol is piloted on a sample of 100 men ,ages 45-59 with total serum cholesterol of 260-299 mg/dl at entry. Following 3months on the medication, the mean cholesterol for the Rx group was 250 mg/dl with a SD of 20mg/dl. what is the 95% confidence interval on the mean for this study?
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| drbin
Forum Guru
Topics: 27
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Choices are
A) 210-290 mg/dl
B) 230-270mg/dl
C) 246-254mg/dl
D) 248-252mg/dl
E) 249-251mg/dl
pls explain.....i got option A as answer but kaplan gives option c is correct and explanation is not given.
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| lampard
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Hi drbin,
Kaplan seems to have got it right,
confidence interval = mean +/- Z score * SEM
Now SEM = SD / sq root of sample size
hence SEM = 20 / sq root of 100
= 20/10
= 2
For 95% CI Zscore = 2
substituting the values
CI = 250 +/- 2 * 2
= 250 +/- 4
ie [ 246,254]
Thanks for the question buddy......
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| drbin
Forum Guru
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thanks lambard...i was doing it wrongly...i thought it as 95% confidence interval means it falls in bwn 2sd of mean so 250+/- 2*20
nw i understand the mistake.....
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| Ivonne
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246-254
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| white-rose
Forum Junior
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Does step 2 ck supply something for you to write on to work these questions out?
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| sherry39
Forum Junior
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aaaaaaaaaaaaaaa...2 times SD on both sides is 95%
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