Hello all,
I am reading and learning the Simulation book of SAS written by Rick Wicklin. In the book I saw a code for power simulation of the t-test, where the effect size is changing (various effect sizes).
I changed the code so it will do a power simulation for the t-test, where the sample size varies and the effect size is constant.
At the end of the original code, there is a procedure to create a graph, where the points and the line are coming from the power procedure and from the simulation (and therefore being compared), these are the lines:
series x=MeanDiff y=Power;
scatter x=Delta y=p;
after I changed the code to my needs, the line disappeared....when I changed the series parameter to p, I got the simulation lines (connection of the points). I don't understand why in the original code the line was plotted and in mine not. I compared the files, they had the same structure. The simulation results were similar. I don't get it. Where did my line go to ?
My code is attached.
Thank you !
proc power;
twosamplemeans power = .
meandiff = 3
stddev = 2
ntotal=10 to 40 by 10;
plot x=N markers=none;
ods output Output=Power;
run;
data PowerSim(drop=i);
call streaminit(321);
do N = 5 to 20 by 5;
do SampleID = 1 to 10000;
c = 1;
do i = 1 to N;
x1 = rand("Normal", 0, 2);
output;
end;
c = 2;
do i = 1 to N;
x1 = rand("Normal", 3, 2);
output;
end;
end;
end;
run;
proc ttest data=PowerSim;
by N SampleID;
class c;
var x1;
ods output ttests=TTests(where=(method="Pooled"));
run;
data Results;
set TTests;
RejectH0 = (Probt le 0.05);
run;
proc freq data=Results noprint;
by N;
tables RejectH0 / out=SimPower(where=(RejectH0=1));
run;
data Combine;
set SimPower Power;
p = percent / 100;
label p="Power";
run;
proc sgplot data=Combine noautolegend;
title "Power of the t Test";
title2 "Samples are N(0,stdev) and N(delta,stdev)";
series x=N y=Power;
scatter x=N y=p;
xaxis label="Sample size";
run;
