SAS way for calculating YoY change

[caveman529]

Dear All:

Could someone tell me how to calculate year to year sales changes when the data is at quarterly interval?

The data looks like:

patient YEAR QTR visit

I do the following

proc sort data=t1 out=t2;

     by patient qtr year;

run;

data t3;

     set t2;

     by patient qtr year;

     if first.patient or first.qtr then

          lagvisit  = .;

     else lagvisit = lag(visit);

run;

But the resulting table is not correct.  Could someone here tell me why?

[Reeza]

Lag shouldn't be used in a conditional statement (if/then).

Conditional Use of LAG - sasCommunity

[caveman529]

Hi, Reeza:

Thanks for the tips.  I'll refrain from using the lag function in if/then situation.  Could you tell me the most efficient way to achieve the task?  I think some kind of proc sql should do the trick, but the syntax would be ugly.

[PGStats · Accepted solution]

All you need is to keep the lag out of the conditional block:

proc sort data=t1 out=t2;

     by patient qtr year;

run;

data t3;

     set t2;

     by patient qtr year;

     lagvisit = lag(visit);

     if first.qtr then lagvisit  = .;

run;

PG

[caveman529]

This works great