Statistics question - doctor_viz

[ArchivalUser]

This one is from one of Goljan's tests:

Text X performed on four normal controls. One standard deviation for the tests is 3 mg/dL. Calculate the reference interval for the test?

Control Test result

control # 1 110 mg/dL
control # 2 90 mg/dL
control # 3 105 mg/dL
control # 4 95 mg/dL

A. 92-108 mg/dL
B. 94-106 mg/dL
C. 97-103 mg/dL
D. 100-113 mg/dL
E. 103-116 mg/dL

If you can explain your choice of answer I would greatly appreciate.

[ArchivalUser]

C. 97-103 mg/dL

[ArchivalUser]

ans: B
exp: Mean: cont1+2+3+4/4: 100
ref interval:95%CI: 100+/- 2SD= (100-6,100=6): (94,106)

[ArchivalUser]

I selected C. Because of the following confidence interval formula:

mean +/- 1.96 x SD/ square root of N

using this formula

100 +/- 1.96 x 3/ square root of 4

100 +/- 3---> 97-103 mg/dL

But Goljan's answer was B, like Seri explained. I'm not sure which one is the right way of solving it.

[ArchivalUser]

OKAY, why 95%CI???

[ArchivalUser]

95% CI because when CI is not mentioned in any stat question we have to take 95% CIas standard. As explained by kaplan. And this is what is mostly done in epidemiological and biostat studies. So when its not mention in a question and they ask for an interval.. even if u hav to find the p-value use 95% as standard that includes 2SD

[ArchivalUser]

thanks seri