topic Proc FREQ: No warning message with expected value <5 in SAS Procedures

Proc FREQ: No warning message with expected value <5

deleted_user — Fri, 09 May 2008 08:23:21 GMT

Hello,

In a population of adolescents, I have to compare distribution of Family Affluence Scale (FAS) according to school level (level). I use the FREQ procedure (with chisq option) to do so, and I wonder why SAS does not warn me in the output of expected values under 5.
I know that the chi-square may be valid (because 5 is an empirical choice and is conservative, especially when degrees of freedom and sample size are high, see Agresti "Categorical Data Analysis" for example), but I don't understand why SAS does not warn me. I thought SAS always printed a warning message when expected values were under 5.

Here are the data if you want to try it yourself.

data bonjour;
input FAS$ level$ n;
cards;
1 1 16
2 1 58
3 1 57
1 2 127
2 2 626
3 2 833
1 3 18
2 3 137
3 3 206
1 4 1
2 4 21
3 4 32
1 5 11
2 5 21
3 5 23
;
run;

Any explanation?

Thank you in advance (and pardon my english!)

Gauthier

Re: Proc FREQ: No warning message with expected value <5

Olivier — Fri, 09 May 2008 11:44:54 GMT

Hi Gauthier.
I do get the Warning message, but only when there more than 20 % cells with expected counts under 5.
See Freq procedure documentation, on the NOWARN option in the TABLES statement :
NOWARN
suppresses the log warning message that the asymptotic chi-square test may not be valid. By default, PROC FREQ displays this log message when more than 20 percent of the table cells have expected frequencies less than five.

Cheers
Olivier

Re: Proc FREQ: No warning message with expected value <5

deleted_user — Fri, 09 May 2008 12:17:34 GMT

Hi Olivier,

I appreciate your help. I recently updated from SAS v 8.2 to v 9.1 and kept on using SAS 8.2 Documentation! I've just checked the NOWARN option in the SAS 9.1 documentation.

Thank you very much!

Gauthier