To investigate an outbreak, epidemiologists usually plot the frequency of cases against the timeline. The dataset may contain a date variable and a time variable. However, if you concatenate date and hour by using the syntax like "datetime = date||hour", it will return the numeric representation of the date and the time. 

Incorrect concatenation

You can use the function DHMS (Date-Hour-Minute-Second) to generate a correctly formatted date-time variable. Although in most cases you don't need minutes and seconds, the full function must be called. You can use formatting to suppress minutes and seconds. For example, to show date, hour, minute, and second, you need datetime18. To show date and hour only, you just need datetime12.

SAS program for plotting an EPI graph

data table1b; set table1;

datetime=dhms(date,0, 0, hour);

format datetime datetime12.;

if datetime NE " " then case = 1;

run;

proc summary data=table1b; class datetime; var case; output out=outbreak sum=sum;

run;

data outbreak; set outbreak;

if _TYPE_ = 0 then delete; run;

goptions reset=all device=actximg;

ods html file="outbreak.html";

proc gchart data=outbreak;

vbar datetime /sumvar=_FREQ_ discrete ; run;

goptions reset=all device=actximg;

quit;

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