Hello,
I finding the association between agents a1,a2,a3 and a4 exposures and lung cancer. Exposed = 1,
unexposed =0. My ref. group(refA) is ids unexposed to any of the agents.
a.I am not sure whether my logistic regression model step 3b is right. I am modelling refA with lung-a1
association., then refA with lung-a2 association,etc.
b. Should the refA be considered as continuous or categorical(as I have done in step 3b of the model)?
Thanks in advance.
ak.
/* Logistic test ref group test*/
data agents_exp;
input id$ a1 a2 a3 a4 lung$ 14-21 income 23-29;
datalines;
os1 1 0 0 1 ca case 45424
os2 1 1 0 0 ca case 52877
os3 0 0 0 0 pop cont 25600
os4 1 0 0 1 pop cont 14888
os5 0 0 0 0 ca case 41036
os6 0 0 0 0 ca case 20365
os7 1 0 1 1 pop cont 16988
os8 0 0 0 0 ca case 100962
os9 1 0 1 0 pop cont 11230
os10 0 0 1 0 ca case 35850
os11 0 1 0 0 pop cont 28700
os12 0 0 0 0 pop cont 46320
os13 1 1 1 1 pop cont 24897
os14 0 0 0 0 pop cont 18966
os15 1 0 0 1 ca case 20540
os16 0 0 1 0 pop cont 150600
os17 1 1 1 1 pop cont 24897
os18 0 0 0 0 pop cont 17999
os19 0 0 0 0 pop cont 22540
os20 0 0 0 0 pop cont 158600
os21 0 0 0 0 pop cont 187365
os22 1 0 1 0 ca case 30580
;
run;
/*Step 1: Finding number of cases and controls unexposed to agents(a1,a2,a3 and a4)*/
proc freq data= agents_exp(where=(sum(a1,a2,a3,a4)=0));
tables lung;
title 'Table 1:Subjects unexposed to any of the 4 agents';
run;
/*Step 2:Using subjects unexposed to any of agents as a ref. group*/
proc sql;
create table t as
select
id, a1, a2, a3,a4,lung, income,
sum(a1,a2,a3,a4)=0 as refB
from agents_exp
;
quit;
proc print data=t;
title 'Table 2: original variables and ref group';
run;
/*proc freq data=t;
tables lung* refB lung*a1;
title 'Table 3: freq of ca case and pop cont for ref group';
run;*/
/*Step 3a: Finding odds ratio estimates for variables including ref.group*/
data logtest; set t;
if lung in ('ca case','pop cont');
run;
/* Step 3b:*/
proc logistic data=logtest;
class refb (param=ref ref ='0');
model lung(event='ca case') = a1 refb;
Title 'Table 3b: Estimates for ref. group';
run;
1 OPTIONS NONOTES NOSTIMER NOSOURCE NOSYNTAXCHECK;
72
73
74 /* Logistic test ref group test*/
75 data agents_exp;
76 input id$ a1 a2 a3 a4 lung$ 14-21 income 23-29;
77 datalines;
NOTE: The data set WORK.AGENTS_EXP has 22 observations and 7 variables.
NOTE: DATA statement used (Total process time):
real time 0.01 seconds
cpu time 0.01 seconds
100 ;
101 run;
102
103 /*Step 1: Finding number of cases and controls unexposed to agents(a1,a2,a3 and a4)*/
104 proc freq data= agents_exp(where=(sum(a1,a2,a3,a4)=0));
105 tables lung;
106 title 'Table 1:Subjects unexposed to any of the 4 agents';
107 run;
NOTE: There were 10 observations read from the data set WORK.AGENTS_EXP.
WHERE SUM(a1, a2, a3, a4)=0;
NOTE: PROCEDURE FREQ used (Total process time):
real time 0.21 seconds
cpu time 0.20 seconds
108 /*Step 2:Using subjects unexposed to any of agents as a ref. group*/
109
110 proc sql;
111 create table t as
112 select
113 id, a1, a2, a3,a4,lung, income,
114 sum(a1,a2,a3,a4)=0 as refB
115 from agents_exp
116 ;
NOTE: Table WORK.T created, with 22 rows and 8 columns.
117 quit;
NOTE: PROCEDURE SQL used (Total process time):
real time 0.01 seconds
cpu time 0.02 seconds
118
119 proc print data=t;
120 title 'Table 2: original variables and ref group';
121 run;
NOTE: There were 22 observations read from the data set WORK.T.
NOTE: PROCEDURE PRINT used (Total process time):
real time 0.38 seconds
cpu time 0.38 seconds
122
123 /*proc freq data=t;
124 tables lung* refB lung*a1;
125 title 'Table 3: freq of ca case and pop cont for ref group';
126 run;*/
127
128 /*Step 3a: Finding odds ratio estimates for variables including ref.group*/
129
130 data logtest; set t;
131
132 if lung in ('ca case','pop cont');
133 run;
NOTE: There were 22 observations read from the data set WORK.T.
NOTE: The data set WORK.LOGTEST has 22 observations and 8 variables.
NOTE: DATA statement used (Total process time):
real time 0.01 seconds
cpu time 0.02 seconds
134
135
136 /* Step 3b:*/
137 proc logistic data=logtest;
138 class refb (param=ref ref ='0');
139 model lung(event='ca case') = a1 refb;
140 Title 'Table 3b: Estimates for ref. group';
141 run;
NOTE: PROC LOGISTIC is modeling the probability that lung='ca case'.
NOTE: Convergence criterion (GCONV=1E-8) satisfied.
NOTE: There were 22 observations read from the data set WORK.LOGTEST.
NOTE: PROCEDURE LOGISTIC used (Total process time):
real time 0.53 seconds
cpu time 0.49 seconds
142
143 OPTIONS NONOTES NOSTIMER NOSOURCE NOSYNTAXCHECK;
155
