Dear SAS Community,   I would like to calculate the mean of a variable for each year and month in a specific time period. I programed a do loop over a proc summary step to do so.    The problem is that I only get back the results for the last iteration of the loop. But I need the results of all the iteration.   I suppose that the loop overwrites the results of former iterations. Do you know a possibility to store the results of each iteration? Or would you suggest a data step with an output statement?   The dataset includes some numeric variables that represent the date as well as a duration variable. For example:    ID eyearmax emonthmax eyear eyear duration 1  2007      6         2007     3      10 1  2007      6         2007     1      15 1  2007      6         2007     6      28 2  2008      5         2007     5      10 3  2007     11         2006     7      11 3  2007     11         2007    11      19 4  2008      1         2008     1       7     %macro test (eyear=, emonth=,); %DO eyear = 2007 %TO 2009; %DO emonth = 1 %TO 12; proc summary data=work.want (where=(eyearmax<=&eyear. and emonthmax<=&emonth.)) nway sum; class id; output out=work.duration sum(duration)=; run; proc summary data=work.duration mean; output out=work.meanduration (drop=_freq_ _type_) mean (duration)=; run; %end; %end; %mend test; %test;   Thank you very much for your help!   Best regards, Sabeth ... View more