Use of CUSUM and Shewhart charts to monitor regional trends of birth defect reports in New York State.
BACKGROUND
Cumulative sum (CUSUM) charts were originally developed for industrial quality control, but may be adapted for the surveillance of health outcome data, such as birth defects. The reported prevalence of birth defects can vary due to differences in case ascertainment, surveillance practices, or true changes in prevalence. We examined the utility of CUSUM and Shewhart charts for detect-ing changes in prevalence of two different birth defect groups. We chose obstructive renal defects because we expected an increase in reporting due to improved diagnosis. We chose oral clefts for comparison because we expected reporting to be unaffected by changes in diagnostic technologies.


METHODS
Data from the New York State Congenital Malformations Registry from 1992-1999 were analyzed using self-starting binomial CUSUM and Shewhart charts for four regions of New York State.


RESULTS
CUSUM charts show that reports of obstructive urinary defects have increased from 1992-1999 in all regions of New York State. Reports of oral clefts increased only on Long Island.


CONCLUSIONS
The CUSUM method proved useful for identifying changes in birth defect reporting and was able to detect the expected increases in obstructive renal defects. The apparent increase is likely due to improvements in diagnostic imaging techniques. In contrast, we only detected an increase in oral clefts on Long Island, which may be related to under report-ing of cases in the earlier years. CUSUM charts are useful in detecting small, sustained increases in prevalences over time while Shewhart charts are easier to interpret and can detect large sharp increases.
Babcock
Gwen D
GD
Bureau of Environmental & Occupational Epidemiology, New York State Department of Health, Troy, 12180, USA. gdb02@health.state.ny.us
Talbot
Thomas O
TO
Rogerson
Peter A
PA
Forand
Steven P
SP
D001719:Birth Certificates; D002972:Cleft Palate / Q000175:diagnosis / Q000453:epidemiology; D000013:Congenital Abnormalities / Q000175:diagnosis* / Q000453:epidemiology*; D003627:Data Interpretation, Statistical; D005568:Forms and Records Control; D005843:Geography; D006753:Hospital Records; D006801:Humans; D007231:Infant, Newborn; D007668:Kidney / Q000002:abnormalities; D008499:Medical Records; D015233:Models, Statistical; D009518:New York; D015995:Prevalence; D011786:Quality Control; D012680:Sensitivity and Specificity; D013997:Time Factors; D016896:Treatment Outcome