Date:         Wed, 28 Oct 2009 19:32:56 -0500
Reply-To:     Lou <lpogoda@HOTMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Lou <lpogoda@HOTMAIL.COM>
Organization: A noiseless patient Spider
Subject:      Re: calculating number of people present given their arrival and
              departure time
Comments: To: sas-l@uga.edu

"bigD" <diaphanosoma@gmail.com> wrote in message
news:08fa14e0-5632-4600-a970-2b9df177d5d6@j9g2000vbp.googlegroups.com...
> Hi,
>
> I have a data set that contains the time a person entered the
> emergency room and the time they left.
> I would like to know how many people were in the emergency department
> for each hour of the day on a weekly basis.

The problem statement could be a little stronger.  For instance, just for
purposes of illustration, let's suppose a day is two hours long - 120
minutes.  How many hourly intervals are you concerned with?  Two, starting
from time 0 and ending at time 120?  Or maybe it's 60, the first interval
starting at time 0 and ending at time 60, the second starting at time 1 and
ending at time 61, etc.?  Or maybe it's only 1, starting at time 30 and
ending at time 90?.

I ask because recently I had to calculate the average number of episodes a
patient had per 28 days over a 84 day interval, and there are 56 periods of
28 days in an 84 day interval.

Whatever the answers to the above, and whatever temporal resolution you need
(hourly intervals by the hour, minute, or second) I probably wouldn't bother
with arrays.  Instead, I'd generate a record for each interval between the
the time a person entered the emergency roon and the time s/he left (one
record an hour, or one record a minute, or one record a second, or whatever)
and then count the total number of records for each timepoint using PROC
MEANS.