@Kilasuelika wrote: I didn't mean creating lagged variables from existing data. Consider an AR(1) model: x[1]=0.5, x[i]=x[i-1]+x[i-2]+rand() At each loop, generate a random value and add it to the previous values. There is only a single variable.   You will have to provide a more complete example to explain what is is you are trying to do.     What you are showing sounds like: data want; x=0.5 ; do i=1 to 10; output; lag1=x; lag2=lag(x); rand=rand('uniform'); x=sum(of lag1 lag2 rand); end; run; Obs x i lag1 lag2 rand 1 0.5000 1 . . . 2 0.5964 2 0.5000 . 0.09637 3 2.0343 3 0.5964 0.5000 0.93795 4 3.2650 4 2.0343 0.5964 0.63433 5 5.8931 5 3.2650 2.0343 0.59379 6 9.8466 6 5.8931 3.2650 0.68843 7 16.4166 7 9.8466 5.8931 0.67684 8 27.1344 8 16.4166 9.8466 0.87119 9 44.5086 9 27.1344 16.4166 0.95770 10 72.3635 10 44.5086 27.1344 0.72051 Which you can do without the LAG() function by just reversing the order of the assignment statements. lag2=lag1; lag1=x; ... View more