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#1
01-05-2013
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 824 Threads: 66 Thanked 462 Times in 298 Posts Reputation: 472
Calculating the 95% Confidence Interval

A study is conducted to evaluate iq for patients with various types of schizophrenia. Twenty patients were dropped from sample because they couldn t complete two or more portions of test. Four additional patients refused to take test. Results for the 100 patients who completed the test showed an average IQ of 110 with a standart 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 85 to 115
D 90 to 130
E 105 to 115
F 106 to 114
__________________
Everything is possible for him who believes (MARK 9:23)
245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad
 The above post was thanked by: neha_subh (01-12-2013)

#2
01-05-2013
 USMLE Forums Scout Steps History: Step 1 Only Posts: 28 Threads: 6 Thanked 3 Times in 3 Posts Reputation: 13

F) 106 to 114
#3
01-05-2013
 USMLE Forums Addict Steps History: CS Only Posts: 127 Threads: 8 Thanked 43 Times in 32 Posts Reputation: 53
B

I would pick B
#4
01-06-2013
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 399 Threads: 45 Thanked 147 Times in 94 Posts Reputation: 157
B

B 70 to 150
#5
01-07-2013
 USMLE Forums Veteran Steps History: 1+CK+CS Posts: 259 Threads: 8 Thanked 115 Times in 78 Posts Reputation: 125

F.

mean +/- 1.96 x SD/square root (N)

110+1.96 x 20/ Squroot 100 = 113.9
100-1.96 x 20/ Squroot 100 = 106

therefore we can say with 95% confidence that the values are btw 106 to 114.
#6
01-07-2013
 USMLE Forums Scout Steps History: 1 + CS Posts: 82 Threads: 10 Thanked 76 Times in 31 Posts Reputation: 86
F

Agreed with above calculations F is my answer also
#7
01-17-2013
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 824 Threads: 66 Thanked 462 Times in 298 Posts Reputation: 472

F is correct
When i was picking the answer made the same mistake of choosing B which is the iq according to test results with two sd deviation above and below
Where as question was asking for CI
__________________
Everything is possible for him who believes (MARK 9:23)
245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad
#8
01-17-2013
 USMLE Forums Addict Steps History: CS Only Posts: 127 Threads: 8 Thanked 43 Times in 32 Posts Reputation: 53

made the same mistake and answered B ..... you are right it's F

 Tags Biostatistics-Epidemiology, Step-1-Questions

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