Hello! I am running a propensity score match and would like some help. My variables are multi-leveled as described below:
age_cat: less than 45, 45-54, 55-64, 65+
region: NE, MW, S, W, Unknown
gendercode: M, F
raceethnicitycode: W, A, B, O
cci_cat4: miss, 0, 1, 2, 3plus
I am using the code below to run the proc psmatch and then to calculate the SMDs based on the proportions. Is this a proper way to do so or should i be using binomal variables? and if I should be, should i do a binomial variable for every level of the multi-level variables? and how do i know if i want to do an exact match and on what variables?
code:
proc psmatch data=redacted;
/* Categorical covariates */
class treatment age_cat region gendercode raceethnicitycode cci_cat4;
/* PS model: include the variables you want balanced */
psmodel treatment(treated='1') =
age_cat
region
gendercode
raceethnicitycode
cci_cat4
;
/* Matching options */
match
method = greedy(k=1) /* 1:1 nearest neighbor */
distance = lps /* caliper applies on logit(PS) */
caliper = 0.2
;
/* Version-friendly balance request */
assess;
/* Output rich diagnostics and flags */
output out=matched_scsdx
ps = _ps_
lps = _lps_
weight = _matchwgt_
matchid = _matchid_;
quit;
data matched_only;
set matched_scsdx;
if _matchwgt_ > 0;
run;
/* -------------------------------
Utility: ensure a weight exists
------------------------------- */
%macro _ensure_weight(in=, weight=, out=, wname=_w_);
data &out.;
set &in.;
%if %length(&weight.) = 0 %then %do; &wname. = 1; %end;
%else %do;
&wname. = &weight.;
if missing(&wname.) then &wname. = 0;
%end;
run;
%mend;
/* -----------------------------------------------------
CATEGORICAL balance (multi-level) with per-level SMD
Produces per-level rows and a MAX_ABS_SMD summary row
----------------------------------------------------- */
%macro balance_categorical(data=, treat=treatment, weight=, catvars=, matched_only=N, out=cat_balance);
%local _base _w_;
%let _base = _catbase_;
%let _w_ = _w_;
/* Subset to matched-only if requested */
%if %upcase(&matched_only.)=Y %then %do;
data &_base._sub;
set &data.;
if _matchwgt_ > 0;
run;
%end;
%else %do;
data &_base._sub; set &data.; run;
%end;
/* Ensure weight */
%_ensure_weight(in=&_base._sub, weight=&weight., out=&_base._w, wname=&_w_.);
/* Loop over categorical variables */
%let _i=1;
%let _var=%scan(&catvars., &_i.);
%do %while(%length(&_var.)>0);
/* Weighted counts by level and treatment */
proc summary data=&_base._w nway;
class &treat. &_var.;
var &_w_.;
output out=&_base._cnt_&_i. (drop=_type_ _freq_) sum=wt_sum;
run;
/* Denominator by treatment */
proc summary data=&_base._w nway;
class &treat.;
var &_w_.;
output out=&_base._den_&_i. (drop=_type_ _freq_) sum=wt_total;
run;
proc sort data=&_base._cnt_&_i.; by &treat.; run;
proc sort data=&_base._den_&_i.; by &treat.; run;
data &_base._props_&_i.;
merge &_base._cnt_&_i.(in=a) &_base._den_&_i.(in=b);
by &treat.;
if a and b;
length level $200 varname $64;
level = vvalue(&_var.);
varname = "&_var.";
run;
proc sql noprint;
create table &_base._wide_&_i. as
select varname, level,
sum(case when &treat.=1 then wt_sum end) as wt_t,
max(case when &treat.=1 then wt_total end) as nt,
sum(case when &treat.=0 then wt_sum end) as wt_c,
max(case when &treat.=0 then wt_total end) as nc
from &_base._props_&_i.
group by varname, level;
quit;
data &_base._smd_&_i.;
set &_base._wide_&_i.;
length phase $8;
if nt>0 then pt=wt_t/nt; else pt=.;
if nc>0 then pc=wt_c/nc; else pc=.;
if n(pt,pc,nt,nc)=4 then do;
p_pool=(pt*nt + pc*nc)/(nt+nc);
if 0<p_pool<1 then smd=(pt-pc)/sqrt(p_pool*(1-p_pool));
else smd=.;
end;
else smd=.;
abs_smd=abs(smd);
keep varname level pt pc smd abs_smd;
run;
/* Max |SMD| summary row */
proc sql noprint;
create table &_base._max_&_i. as
select varname, 'MAX_ABS_SMD' as level length=12,
. as pt, . as pc, . as smd, max(abs_smd) as abs_smd
from &_base._smd_&_i.
group by varname;
quit;
data &_base._out_&_i.; set &_base._smd_&_i. &_base._max_&_i.; run;
%let _i=%eval(&_i.+1);
%let _var=%scan(&catvars., &_i.);
%end;
%if %eval(&_i.-1) > 0 %then %do;
data &out.; set &_base._out_:; run;
%end;
%else %do;
data &out.; length varname $64 level $200 pt pc smd abs_smd 8.; stop; run;
%end;
proc datasets library=work nolist;
delete &_base._: ;
quit;
%mend;
/* ----------------------------------------------
CONTINUOUS balance: SMD using means/pooled SD
---------------------------------------------- */
%macro balance_continuous(data=, treat=treatment, weight=, contvars=, matched_only=N, out=cont_balance);
%local _base _w_;
%let _base = _contbase_;
%let _w_ = _w_;
%if %upcase(&matched_only.)=Y %then %do;
data &_base._sub;
set &data.;
if _matchwgt_ > 0;
run;
%end;
%else %do;
data &_base._sub; set &data.; run;
%end;
%_ensure_weight(in=&_base._sub, weight=&weight., out=&_base._w, wname=&_w_.);
%let _i=1;
%let _var=%scan(&contvars., &_i.);
%do %while(%length(&_var.)>0);
proc means data=&_base._w nway;
class &treat.;
var &_var.;
weight &_w_.;
output out=&_base._stats_&_i. (drop=_type_ _freq_) mean=mean var=var;
run;
proc sql noprint;
create table &_base._smd_&_i. as
select "&_var." as varname length=64,
max(case when &treat.=1 then mean end) as mean1,
max(case when &treat.=0 then mean end) as mean0,
max(case when &treat.=1 then var end) as var1,
max(case when &treat.=0 then var end) as var0
from &_base._stats_&_i.;
quit;
data &_base._smd_&_i.;
set &_base._smd_&_i.;
length level $200;
level = ''; /* no levels for continuous */
if n(var1,var0)>0 then do;
denom=sqrt((var1+var0)/2);
if denom>0 then smd=(mean1-mean0)/denom;
else smd=.;
end;
else smd=.;
abs_smd=abs(smd);
keep varname level mean1 mean0 smd abs_smd;
run;
%let _i=%eval(&_i.+1);
%let _var=%scan(&contvars., &_i.);
%end;
%if %eval(&_i.-1) > 0 %then %do;
data &out.; set &_base._smd_:; run;
%end;
%else %do;
data &out.; length varname $64 level $200 mean1 mean0 smd abs_smd 8.; stop; run;
%end;
proc datasets library=work nolist;
delete &_base._: ;
quit;
%mend;
/* ---------------------------------------------------
WRAPPER: Creates combined balance tables
- inputdata: dataset (pre or post)
- treat: treatment var (default: treatment)
- weight: leave blank for PRE; set _matchwgt_ for POST
- matched_only: Y to restrict POST to matched rows
- catvars: list of categorical variables
- contvars: list of continuous variables
- out: combined output table
--------------------------------------------------- */
%macro create_balance(inputdata=,
treat=treatment,
weight=,
matched_only=N,
catvars=,
contvars=,
out=balance_out);
%balance_categorical(data=&inputdata., treat=&treat., weight=&weight.,
catvars=&catvars., matched_only=&matched_only.,
out=_cat_bal_);
%balance_continuous(data=&inputdata., treat=&treat., weight=&weight.,
contvars=&contvars., matched_only=&matched_only.,
out=_cont_bal_);
data &out.;
length Category $20;
set _cat_bal_(in=a) _cont_bal_(in=b);
if a then Category='Categorical';
else if b then Category='Continuous';
run;
proc datasets library=work nolist; delete _cat_bal_ _cont_bal_; quit;
%mend;
/* PRE-match: unweighted */
%create_balance(
inputdata = combined_demog_cci_final_2_NOU,
treat = treatment,
weight = , /* none */
matched_only= N,
catvars = age_cat region gendercode raceethnicitycode cci_cat4,
contvars = ageatendyear CCI,
out = balance_pre
);
/* Print summary: per-level and max |SMD| rows included */
title "PRE-match Balance (SMDs)";
proc print data=balance_pre noobs;
var Category varname level pt pc mean1 mean0 smd abs_smd;
format pt pc percent8.2 smd abs_smd 6.3;
run;
/* POST-match: weighted & restricted to matched-only */
%create_balance(
inputdata = matched_only,
treat = treatment,
weight = _matchwgt_,
matched_only= Y,
catvars = age_cat region gendercode raceethnicitycode cci_cat4,
contvars = ageatendyear CCI,
out = balance_post
);
