Test for trend using median values

[Marjolein]

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.

[Ksharp]

Check PROC CATMOD which can perform ANOVA or REG analysis.

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

[Marjolein]

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!

[Ksharp]

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 .........

[SteveDenham · Accepted solution]

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

[Marjolein]

Thanks! It worked 😄