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#1
05-04-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,353 Threads: 94 Thanked 877 Times in 507 Posts Reputation: 890
Calculating the 95% Confidence Interval?

100 students took a medical school exam and the average score was 110 with a standard deviation of 20. Which of the following is the best estimate of the 95% confidence interval for the sample?

a. 70 to 130
b. 70 to 150
c. 90 to 130
d. 105 to 115
e. 106 to 114
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 The above post was thanked by: Casandra (05-04-2012)

#2
05-04-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610

E) 106-114

Mean = 110
SD = 20
n (sample size) = 100

For 95%, use Confidence Interval of 1.96 or 2 (to simplify calculation)

Mean +/- CI * (SD/ sqrt of n)
= 110 +/- 2*(20/sqrt100)
= 110 +/- 2*(20/10)
= 110 +/- 2*(2)
= 110 +/- 4
= 110-4 to 110+4
= 106-114
 The above post was thanked by: Casandra (05-04-2012), DocSikorski (05-04-2012), Kabutar111 (05-09-2012)
#3
05-04-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,353 Threads: 94 Thanked 877 Times in 507 Posts Reputation: 890

Quote:
 Originally Posted by Hope2Pass E) 106-114 Mean = 110 SD = 20 n (sample size) = 100 For 95%, use Confidence Interval of 1.96 or 2 (to simplify calculation) Mean +/- CI * (SD/ sqrt of n) = 110 +/- 2*(20/sqrt100) = 110 +/- 2*(20/10) = 110 +/- 2*(2) = 110 +/- 4 = 110-4 to 110+4 = 106-114
I see someone is revising biostats hehe =)

I got this one wrong, only 23% got it right in Kbank, I believe its worth posting in here.
Great explanation!
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Ambition is a dream with a V8 engine. EP
 The above post was thanked by: Hope2Pass (05-04-2012)

#4
05-04-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610

Quote:
 Originally Posted by DocSikorski I see someone is revising biostats hehe =) I got this one wrong, only 23% got it right in Kbank, I believe its worth posting in here. Great explanation!
Thanks!

I remember doing a question on CI in the Qbank about 2-3 weeks ago and I got it wrong...so I knew my stuff and made sure I don't make same mistake twice
 The above post was thanked by: Dr. Mexito (05-04-2012)
#5
05-04-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 647 Times in 409 Posts Reputation: 657

damn, i immediately jumped at B :/ lol
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#6
05-04-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 720 Threads: 217 Thanked 552 Times in 309 Posts Reputation: 562

70 - 150

 Tags Biostatistics-Epidemiology, Step-1-Questions

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