topic Re: Test for trend using median values in Statistical Procedures

Test for trend using median values

Marjolein — Mon, 24 Oct 2016 12:51:19 GMT

Hi all,

I'm trying to perform a test for trend in an ANOVA procedure. For example: I have 4 categories of a blood parameter (from which I obtained the median values), and I want to see whether some kind of baseline characteristic (e.g. age) increases linearly with this blood parameter.

This is what I've tried:

PROC GLM DATA=my.data;

CLASS bloodparameter;

MODEL age = bloodparameter;

CONTRAST "linear trend" bloodparameter 1.71 2.14 2.63 3.62 ;

MEANS bloodparameter;

RUN;

I searched on the internet and I saw the following code for the linear trend test: x -3 -1 1 3.

Therefore I replaced it with the median values, since they are not equally spaced.

However, SAS says the trend is not estimatable. What am I doing wrong?

Thanks a lot in advance.

Kind regards, M.

Re: Test for trend using median values

Ksharp — Tue, 25 Oct 2016 09:59:06 GMT

Check PROC CATMOD which can perform ANOVA or REG analysis.

And there is already an example like yours about social ability in documentation.

Re: Test for trend using median values

Ksharp — Wed, 26 Oct 2016 02:39:24 GMT

Or you can just check the correlation coefficient of row and column variable by PROC FREQ.

Check statistical GAMMA,Kendall's Tau,Somer's D .........

Re: Test for trend using median values

Marjolein — Wed, 26 Oct 2016 12:57:57 GMT

I indeed did an ANOVA and I imputated the median values as new variable, and put this in the class statement! So it's solved! Thanks for the input!

Re: Test for trend using median values

SteveDenham — Mon, 07 Nov 2016 14:18:25 GMT

There are several on-line calculators that can give the coefficients for a linear trend with unequal spacing. The key is that the coefficients in a CONTRAST statement must sum to zero. You can do this by subtracting the mean of the values you have from each individual value. In this case, I got -0.815 -0.385 0.105 1.095. Try plugging in those values where you currently have 1.71 2.14 2.63 3.62,

Steve Denham

Re: Test for trend using median values

Marjolein — Fri, 04 Nov 2016 10:19:38 GMT

Thanks! It worked 😄