## number of days in the study period

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Regular Contributor
Posts: 182

# number of days in the study period

Hi! I need help calculating the number of actual days a person was in my 5 year study.  So, looking accross observations, I need to calculate number of days between the first encounter date 'encdate' and last encounter date by 'patientid'.

Assistance is apprecited!

Accepted Solutions
Solution
‎06-08-2016 10:21 AM
Super User
Posts: 6,751

## Re: number of days in the study period

Here's one approach.

proc summary data=have nway;

class patientid;

var encdate;

output out=durations (keep=patientid firstday lastday) min=firstday max=lastday;

run;

This gives you a data set with three variables in it, and one observation per patientid.  You can use that in a DATA step, and apply whichever formula you wish:

duration = lastday - firstday;

duration = lastday - firstday + 1;

The SQL programmers out there can do this in one step, but SQL isn't my strong point.

All Replies
Super User
Posts: 23,663

## Re: number of days in the study period

Please post sample input and output data.

Solution
‎06-08-2016 10:21 AM
Super User
Posts: 6,751

## Re: number of days in the study period

Here's one approach.

proc summary data=have nway;

class patientid;

var encdate;

output out=durations (keep=patientid firstday lastday) min=firstday max=lastday;

run;

This gives you a data set with three variables in it, and one observation per patientid.  You can use that in a DATA step, and apply whichever formula you wish:

duration = lastday - firstday;

duration = lastday - firstday + 1;

The SQL programmers out there can do this in one step, but SQL isn't my strong point.

Super User
Posts: 13,498

## Re: number of days in the study period

Minor change to @Astounding solution:

output out=durations (keep=patientid firstday lastday) range=;

Range will basically do the max-min.

New Contributor
Posts: 2

## Re: number of days in the study period

how can i get sas software

New Contributor
Posts: 2

Super User
Posts: 23,663

## Re: number of days in the study period

[ Edited ]

@kvemulapalli571

1. Please post your questions in a new discussion rather than in someone else's question

2. Google "SAS University Edition" -> This is a free version of SAS available for learning purposes only. You need a 64bit machine.

Or use SAS Academics on Demand -> Independent Learners option.

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