Control group characteristics and study outcomes: empirical data from a study on mortality of patients with type 2 diabetes mellitus in Dutch general practice.
OBJECTIVE
Control group characteristics as comorbidity and chronic psychosocial problems may play an important part in study outcomes. A primary care data base was used to quantify the effects of varying the case mix of participants.


METHODS
Historical cohort study.


METHODS
Data were collected from 1967-1996 in four Dutch general practices performing the Continuous Morbidity Registration Nijmegen.


METHODS
All newly diagnosed type 2 diabetic patients in the period 1967-1989 fulfilling the WHO criteria (n = 265); for each type 2 diabetic patient a control was matched for practice, sex, age, and social class; from these controls subgroups were selected based on the absence of different types of morbidity; these subgroups were also matched for practice, sex, age, and social class.


RESULTS
The relative risk of mortality in type 2 diabetic patients in comparison with various subsets of controls ranged from 1.33 (95% CI 0.97, 1.81) to 2.16 (95% CI 1.46, 3.20).


CONCLUSIONS
Control group characteristics as comorbidity and chronic psychosocial problems turned out to influence the risk estimation in a cohort study. General practice data enhance the study of these aspects.
Department of General Practice and Social Medicine, University of Nijmegen, The Netherlands.
W J
WJ
de Grauw
H J
HJ
van den Hoogen
E H
EH
van de Lisdonk
W H
WH
van Gerwen
C
C
van Weel
D002318:Cardiovascular Diseases / Q000453:epidemiology; D016022:Case-Control Studies; D002908:Chronic Disease; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000401:mortality*; D005069:Evaluation Studies as Topic; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009426:Netherlands / Q000453:epidemiology; D012044:Regression Analysis; D018570:Risk Assessment; D012307:Risk Factors; D018571:Sentinel Surveillance