How to calculate difference between dates by group

[jtscheirer]

Hello,

I have data that resembles the below, and need to calculate the average time (in months) between dates in the Event_date column, grouped by Subject_ID. In other words, for each subject in the data, I need to know the average number of months between events relevant to that subject. Each subject has a different number of events that are associated with them. Is there a relatively straightforward way to do this? I know how to do this in R, but I'm relatively new to SAS and haven't been able to figure out a solution just yet.

Thanks in advance for any help this community can provide!

Subject_ID	Event_date
1	Date_1
1	Date_2
1	Date_3
2	Date_1
2	Date_2
3	Date_1
3	Date_2
3	Date_3
3	Date_4
3	Date_5
3	Date_6
4	Date_1
4	Date_2
5	Date_1
5	Date_2
5	Date_3
5	Date_4
6	Date_1
6	Date_2

[Ksharp]

What do you mean by "the average number of months between events"?

Can you post some real data and the desired output you are looking for ?

data have;
input id date date9.;
format date date9.;
cards;
1 01jan2010
1 01mar2011
1 01feb2012
2 01nov2010
2 01mar2011
2 01dec2014
;

proc sort data=have out=temp;
by id date;
run;
data temp;
 set temp;
 by id;
 n_month=intck('month',lag(date),date,'c');
 if first.id then call missing(n_month);
run;
proc summary data=temp;
by id;
var n_month;
output out=want mean=;
run;