Biostat Macro Library

Calculate Standard Deviation and Standard Error

%Macro stdev(anary,start,stop,mmean,sstdev,sstderr);
    *Macro returns the mean and standard deviation for the elements start-stop in array anary;
    ssum=0;
    Do ii=&start To &stop;
        ssum=ssum+&anary{ii}; *find the sum;
    End;
    &mmean=ssum/(1.0+&stop-&start); *calculate the mean;
    &sstdev=0;
    Do ii=&start To &stop;
        &sstdev=&sstdev+(&anary{ii}-&mmean)**2; *sum the squared differences from the mean;
    End;
    &sstdev=Sqrt(&sstdev/(&stop-&start)); *calculate the square root of the sum / n-1;
    &sstderr=&sstdev/Sqrt(1.0+&stop-&start); *calculate standard error;
%Mend stdev;

Data work.A; *example to call the macro;
    Retain n 0 x1-x10;
    Array x{10};
    n=n+1;
    Input x{n};
    %stdev(x,1,n,mean,stdev,stderr);
    Output;
    Cards;
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Run;