topic Re: Post-hoc comparisons_obtaining p value for in-between group comparisons in Statistical Procedures

Post-hoc comparisons_obtaining p value for in-between group comparisons

Ashwini_uci — Tue, 03 Feb 2015 22:05:58 GMT

Hi,

I am working on a cross table, for instance for the cross table Hospital regions vs ARF-NoARF hospitalizations, it would be 2 x 4 cross table and the p value yielded is applicable to the whole tables combined. How do I get the p values for difference between ARF-NOARF admissions for each region separately, the poct-hoc comparisons?

I am attaching a part of the table and its figure here to this post.I want the p values for the highlighted #s in the table. I have also plotted them on the graph next to the table. All I need is the p values for the red/blue bars for each region.

The overall p value that’s shown in the table is the combined p value. But in the graph you see that the ARF and NIS %s are very different for northeast and South regions but NOT very different for Midwest and West regions. So how do I get those p values exactly, separate for each region from this table that would allow me say if they are significant or not?

SO basically the code I have used is below and that’s how I got the table below and I created the graph. You can take a look at the Figure 3 in that paper and read the description right below it.

proc freq;

table arf hospitalization *region /chisq;

run;quit;

Any help would be greatly appreciated!

Thanks,

Ashwini

Re: Post-hoc comparisons_obtaining p value for in-between group comparisons

SteveDenham — Wed, 04 Feb 2015 13:58:31 GMT

Try this:

proc freq;

by region;

tables arf hospitalization/binomial;

run;

Steve Denham

Re: Post-hoc comparisons_obtaining p value for in-between group comparisons

Ashwini_uci — Thu, 05 Feb 2015 21:49:46 GMT

Thanks very much Steve.! I tried the above code by using another example.Regionwise afib hospitalizations. I am attaching the output to the original posts. I am not sure how to interprete the results though.

For this analyses, I am referring to a published article and I've highlighted the part that I am trying to do for my analyses.In that paper, they have mentioned the posthoc comparisons in 3 figures which I have highlighted in the article and attached it to the oiginal post. I have made similar graphs and and my results are quite similar to theirs so I would like to do the posthoc comparisons as well. I have also attached my own results in the original post.

Please take a look and if yo could advise on how I can obtain those p values; for the post-hoc comparisons ,that would bevery helpful!

Re: Post-hoc comparisons_obtaining p value for in-between group comparisons

SteveDenham — Fri, 06 Feb 2015 13:20:58 GMT

Well, for each region you get: proportion in each category, the asymptotic standard error, confidence bounds, and a test of whether the proportion is equal to 0.5, which is equivalent to asking whether the categorization yields a different proportion than simple randomization.

So the procedure in the paper most likely did the following:

proc freq;

tables region*arf_hospitalization/chisq;

weight KIDwt;

run;

If that is significant, then follow-up with pairwise comparisons:

proc freq;

where region=1 or region=2;/* This coding will depend on how regions are coded*/

tables region*arf_hospitalization/chisq;

weight KIDwt;

run;

and then stepping through all pairwise comparisons of region. If there are a lot of comparisons, you may need to consider passing the raw p values to PROC MULTTEST to get adjusted p values, but it does not appear that Miyake et al. did that.

Steve Denham