Dear Madam/Sir,   I would like to standard deviation of cash flow (cf) in the past three years (twelve quarters) using the data example below. The modified code below is not working well. Any advice will be highly appreciated.   data want; set have; by gvkey; array t {12} _temporary_; if first.gvkey then call missing(of t{*}); do fy=sum(lag(quarter),1) to quarter-1; t{1+mod(fy,12)}=.; end; t{1+mod(fyear,12)}=cf; if n(of t{*})>1 then cfstd=std(of t{*}); run;     gvkey         year      quarter     cf 1004 1988 1 -0.0032 1004 1988 2 -0.0035 1004 1988 3 -0.0119 1004 1988 4 0.00026 1004 1989 1 -0.018 1004 1989 2 0.00369 1004 1989 3 0.01763 1004 1989 4 0.04986 1004 1990 1 0.02346 1004 1990 2 0.02906 1004 1990 3 0.10553 1004 1990 4 0.09709 1004 1991 1 -0.0015 1004 1991 2 -0.0132 1004 1991 3 -0.0153 1004 1991 4 0.02229 1004 1992 1 -0.0018 1004 1992 2 0.0007 1004 1992 3 0.01478 1004 1992 4 0.04602 1004 1993 1 0.01721 1004 1993 2 0.02124 1004 1993 3 -0.0203 1004 1993 4 0.01604 1008 1994 1 -0.0216 1008 1994 2 -0.0355 1008 1994 3 -0.0076 1008 1994 4 0.03583 1008 1995 1 0.01708 1008 1995 2 0.01056 1008 1995 3 0.03202 1008 1995 4 0.05655 1008 1996 1 0.02278 1008 1996 2 0.02372 1008 1996 3 0.0076 1008 1996 4 0.018 1008 1997 1 0.00274 1008 1997 2 -0.0305 1008 1997 3 -0.0153 1008 1997 4 0.03404   Thank you so much for your help. Joon1 ... View more