topic Re: Cost data with proc genmod in Statistical Procedures

Cost data with proc genmod

SASHELP84 — Tue, 07 Jul 2020 17:48:16 GMT

Hi,

I am trying to get the marginal difference in mean cost and 95% CI for an exposure with 5 groups using a GLM with log link and gamma distribution and have tried lsmeans, estimate, etc but all the results are off. I also tried %NLEstimate but it did not work for me.

Any advice?

Thank you!

proc genmod data=t0 ;
class expa(ref="1") agegroup(ref='1') female(ref='1') region(ref='1') flag_ad(ref='0') flag_ohter_comb(ref='0')/param=ref;
model total_cost=expa agegroup female region flag_ad flag_ohter_comb/dist=gamma link=log type3;
store p1;
output out=c predicted=pred_c;
run;

expa is a categorical variable with 5 levels

I am trying to get the exponential transformed cost and 95% CI for expa= 2 vs. 1, 3 vs. 1, 4 vs. 1, 5 vs. 1

/*Test incorrect results*/
proc genmod data=t0 ;
class expa(ref="1") agegroup(ref='1') female(ref='1') region(ref='1') flag_ad(ref='0') flag_ohter_comb(ref='0')/param=ref;
model total_cost=expa agegroup female region flag_ad flag_ohter_comb/dist=gamma link=log type3;
estimate 'expa=1' intercept 1 expa 1 agegroup 1 female 1 region 1 flag_ad 0 flag_ohter_comb 0 / exp;
estimate 'expa=2' intercept 1 expa 2 agegroup 1 female 1 region 1 flag_ad 0 flag_ohter_comb 0 / exp;
estimate 'expa=3' intercept 1 expa 3 agegroup 1 female 1 region 1 flag_ad 0 flag_ohter_comb 0 / exp;
estimate 'expa=4' intercept 1 expa 4 agegroup 1 female 1 region 1 flag_ad 0 flag_ohter_comb 0 / exp;
estimate 'expa=5' intercept 1 expa 5 agegroup 1 female 1 region 1 flag_ad 0 flag_ohter_comb 0 / exp;
lsmestimate expa "2 vs. 1" 2 1 / cl;
lsmestimate expa "3 vs 1" 3 1/ cl;
lsmestimate expa "4 vs 1" 4 1/ cl;
lsmestimate expa "5 vs 1" 5 1/ cl;
run;

Re: Cost data with proc genmod

ChrisNZ — Fri, 10 Jul 2020 02:02:28 GMT

Moved to STAT forum in the hope you'll get an answer there.

Re: Cost data with proc genmod

SteveDenham — Fri, 10 Jul 2020 12:33:14 GMT

I am almost certain that the coefficients you are supplying are not what you want.

Why not do something like:

lsmeans expa/diff=control cl exp;

This will construct the differences between each noncontrol level and the control level (which defaults to the first level) and the confidence bounds, followed by exponentiating each of those.

For the lsmestimate statements, you need to construct differences rather than the sums of treatment 2 and multiples of treatment 1. Try

lsmestimate expa "2 vs 1" -1 1  0 0 0/ cl exp;
lsmestimate expa "3 vs 1" -1 0 1 0 0/ cl exp;
lsmestimate expa "4 vs 1" -1 0 0 1 0/ cl exp;
lsmestimate expa "5 vs 1" -1 0 0 0 1/ cl exp;

This should give results that are identical to the lsmeans diffs.

SteveDenham

Re: Cost data with proc genmod

StatDave — Fri, 10 Jul 2020 13:16:39 GMT

The NLEstimate macro could certainly work, but since you just want differences of means it would be easier to use the NLMeans macro.

proc genmod data=t0 ;
  class expa(ref="1") agegroup(ref='1') female(ref='1') region(ref='1') flag_ad(ref='0') flag_ohter_comb(ref='0')/param=ref;
  model total_cost=expa agegroup female region flag_ad flag_ohter_comb/dist=gamma link=log type3;
  store p1;
  run;
proc plm restore=pl;
  lsmeans expa / e ilink diff exp;
  ods output coef=coeffs;
  run;
%NLMeans(instore=pl, coef=coeffs, link=log, title=Difference of EXPA means)