st: cusum for count data

[Rachel Savage <Rachel.Savage@oahpp.ca>]

Hi All

We are analysing surveillance data (aggregate counts of cases by day) and wanted to apply CUSUM methodology to detect aberrant events.

In SAS, you can specify key parameters to be used in the calculation of your CUSUM (mean, std dev, shift in mean you wish to detect, along with the threshold parameter) as follows below.  SAS will then plot the cusum and identify where the cusum goes above the set threshold.

proc cusum data=example;
xchart cases*date/
scheme=onesided 
mu0=4 
sigma0=0.7 
delta=1.5 
k=0.75 
h=4
Outtable=cusum_output;
run;