At 03:55 AM 12/3/2006, Ethan Johnsons wrote:
>I have the clinical study data.
>
> Year 0 Year 3
>Retinol (nmol/L) N Mean +-sd Mean +-sd
>Vitamin A group 73 1.89+-0.36 2.06+-0.53
>Trace group 57 1.83+-0.31 1.78+-0.30
>
>where N is the number of male for the clinical study.
>
>I want to test if the mean serum retinol has increased over 3 years
>among subjects in the vitamin A group.
If You desire check mean serum retinol has increased over 3 years in
vitamin A group.
You may use t.test
Look this example:
#Generate random Data
set.seed(123)
VitA1<-rnorm(73,1.89,.36)
Trace1<-rnorm(57,1.83,0.31)
VitA2<-rnorm(73,2.06,.53)
Trace2<-rnorm(57,1.78,0.30)
# Calculate diference Year 3 - Year 0
dVitA<-VitA2-VitA1
dTrace<-Trace2-Trace1
# Testing diference
t.test(dVitA,dTrace)
Welch Two Sample t-test
data: dVitA and dTrace
t = 2.2762, df = 117.746, p-value = 0.02464
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
0.02756874 0.39659494
sample estimates:
mean of x mean of y
0.15905162 -0.05303022
Bernardo Rangel Tura, MD, Phd
National Institute of Cardiology Laranjeiras
Rio de Janeiro Brazil