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#1
07-15-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,088 Times in 1,047 Posts Reputation: 2108
The upper limit of Confidence Interval

What is the upper limit of the two-sided 90% confidence interval for the following sample: X=14, 19, 15, 20, 26, 21?

(a) 21.791
(b) 23.090
(c) 22.040
(d) 22.749

#2
07-15-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 646 Threads: 52 Thanked 761 Times in 256 Posts Reputation: 772

long calculation...

first calculate the mean of the given numbers which rounded off comes to 19.2
the subtract the mean from each number.... and square all the answers you get.

so now you have the sum of (X-X')^2 which comes out to 94.84

divide that by n-1 and then do the square root of that number ....

then substitute in the formula

where

CI == mean +/- Z [SD/square root of N]

because we want the CI at 90%... Z value is 1.5 (roughly)

so finally.... answer comes to approx (a) 21.791
(maybe another close answer choice cos i've rounded up alot of decimals.. but i think this is the way to do it? )

 Tags Biostatistics-Epidemiology, Step-2-Questions

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