Diabetes Care, Vol 23, Issue 6 759-764, Copyright © 2000 by American Diabetes Association
Capture-recapture method in the epidemiology of type 2 diabetes: a contribution from the Verona Diabetes Study
G Verlato and M Muggeo
Medical Statistics, University of Verona Medical School, Italy. giuseppe@biometria.univr.it
OBJECTIVE: The present investigation used data from the Verona Diabetes
Study to verify a main assumption of the capture-recapture method (source
independence) and to characterize the subgroup of known diabetic patients
missed by all sources whose number is estimated by the capture-recapture
method. RESEARCH DESIGN AND METHODS: The Verona Diabetes Study identified
7,148 type 2 diabetic patients on 31 December 1986 using 3 different
sources: family physicians, a diabetes center, and a drug prescription
database. Completeness of ascertainment was estimated with traditional
methods based on the hypergeometric distribution and with a log-linear
model. RESULTS: Identification sources were not independent because the
drug prescription database was positively related to family physicians and
negatively related to the diabetes center (P < 0.001). Thus,
completeness of ascertainment was overestimated (87.5% [95% CI 86.3-88.8])
when using only family physicians and the drug prescription database and
underestimated (45.9% [43.9-48.1]) when using only the diabetes center and
the drug prescription database. Because of characteristics contributing to
variable "catchability" (probability of ascertainment), the estimated
proportion of ascertainment increased with increasing time since diagnosis
from 65.6% in the first tertile (<6 years) to 91.5% in the third tertile
(>12 years); moreover, the ascertainment was estimated to be nearly
complete (97.9%) for insulin-treated patients and scanty (28.9%) for
diet-treated patients. CONCLUSIONS: Because identification sources are
likely to be dependent, the capture-recapture method should be used with
caution in diabetes epidemiology and possibly when at least 3 sources are
available. The subgroup of diabetic patients whose existence is inferred by
this technique likely consists of newly diagnosed patients with mild
disease severity.