[R] prop.trend.test issue

Ethan Johnsons ethan.johnsons at gmail.com
Mon Dec 4 15:37:55 CET 2006


On 12/4/06, Bernardo Rangel tura <tura at centroin.com.br> wrote:
> 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
>
>

Thank you so much.  It is clear now.

ej




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