Rob van Hest Capture-recapture Methods in Surveillance - RePub ...

Methodology of capture-recapture analysis
minimise violation of the closed population assumption. Violation of the homogeneity
assumption can be handled by stratification of the population into more homogeneous
strata, perform capture-recapture analysis for each of the distinct subgroups and
subsequently add the results for the total estimate An alternative is to include covariates
with a strong relationship to the probability of capture in a log-linear covariate capturerecapture
model. 15,16 A third approach, if possible, is to model the heterogeneity, e.g. with
logistic regression. 17,18 Violation of the independency assumption can be partially
identified and controlled when more than two sources are linked, allowing for sources to
be examined pair-wise, i.e. two at a time. 5 In the absence of source dependence the
possible pair-wise capture-recapture estimates of the total number of cases should be
reasonably similar. Positive dependence between two of the lists can be suspected when a
pair-wise estimate is considerably lower than the other pair-wise estimates. In the threesource
capture-recapture approach according to Fienberg, pair-wise dependencies can be
incorporated in the log-linear model as interactions. In case of three sources, three-way
interaction, i.e. dependence between all three registers, is assumed to be zero, or, in case
of multiple sources, highest-order interaction, i.e. dependence between all sources, is
assumed to be zero. When interactions are incorporated in the log-linear model, especially
when all interactions are incorporated in a so-called ‘saturated’ model, with no degrees of
freedom –df’s– left, three-way interaction cannot be excluded and the assumption that
this interaction is zero has been called an “act of faith”. 10,12 The positive predictive value
can be increased through an adequate and unambiguous case-definition, uniform for all
sources, cross-validation through record-linkage with other related data sources and
identification and exclusion of false-positive cases. Examination of a period of time before
and after the study episode can correct for late registration
2.1.3 The two-source capture-recapture model
A two-source capture-recapture problem with registers A and B can be graphically
presented as in table 2.1.
Table 2.1 The two-source capture-recapture problem
Register B
Register A Not observed Observed Total register A
Not observed nˆ 00
n01 Observed n10 n11 NA Total register B NB The numbers of cases only on register A, only on register B, on both registers and on
neither register, can be expressed as n10, n01, n11 and nˆ 00 respectively. The number of
cases on register A, NA, is n10 + n11 and the number of cases on register B, NB, is n01 + n11. The total observed population on at least one register, the case-ascertainment, equals n10 +
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