Using Lag function

[ChuksManuel]

Hello programmers,

How can i use the lag function to print out patients that have 15% or more reduction in systolic BP and 8% or more reduction in diastolic BP between visits 1 and 5.

Thanks!

[ChuksManuel]

DATA five;
SET four;
lag_systolic = lag(systolic);
dif_systolic = systolic - lag_systolic;
per_incr_sys = (dif_systolic/lag_systolic)*100;
RUN;
proc print; run;

data six;
set five;
lag_diastolic = lag(diastolic);
dif_diastolic= diastolic- lag_diastolic;
per_incr_dia = (dif_diastolic/lag_diastolic)*100;
run;
proc print; run;

data seven;
set six;
if per_incr_sys =< -15 and per_incr_dia =<-8 then output;
run;
proc print; run;

[Reeza]

My default would be to recommend RETAIN or data step merge instead.

You could use LAG4/LAG5 but then you need to be absolutely sure you'll have the correct number of records for each ID (5 visits).

You may also want to look into the DIF() function instead of LAG() same idea, except it differences automatically. Same concept though, need to be sure you have the correct number of observations.

[Reeza · Accepted solution]

This paper is a good reference for leads/lags and how they work.
https://support.sas.com/resources/papers/proceedings16/11221-2016.pdf