How to estimate the population that is covered by community pharmacies? An evaluation of two methods using drug utilisation information.
OBJECTIVE
Pharmacy-dispensing data are valuable sources of drug information, but the population that is covered by the pharmacies is often difficult to determine. We evaluated two methods using drug utilisation information to estimate the population size: a drug-use-based extrapolation of a known part of the population and a capture-recapture estimation without any prior knowledge of the population.


METHODS
Using pharmacy-dispensing data of three towns with known populations in the Netherlands, we estimated age-and-sex specific population sizes by extrapolating the proportion of drug-using inhabitants. In addition, we applied two-source and three-source capture-recapture models with all combinations of the following drug groups as different sources: anti-asthmatics, analgesics, antibiotics and anti-histamines.


RESULTS
Drug-use-based extrapolation resulted in the best estimates with the least variability. All capture-recapture models provided underestimations of the true population. Three-source capture-recapture resulted in better average estimates than two-source capture-recapture, but also had more variability.


CONCLUSIONS
If a part of the population is known, and if there is reason to assume that drug utilisation patterns do not vary within the region, it is best to use drug-use-based extrapolation. In all other situations capture-recapture may be considered, with as main limitation that we found all models to underestimate the population considerably.
Schirm
Eric
E
Department of Social Pharmacy, Pharmacoepidemiology and Pharmacotherapy, Groningen University Institute for Drug Exploration, University of Groningen, Groningen, The Netherlands.
Monster
Taco B M
TB
de Vries
Robin
R
van den Berg
Paul B
PB
de Jong-van den Berg
Lolkje T W
LT
Tobi
Hilde
H
D017677:Age Distribution; D003157:Community Pharmacy Services / Q000706:statistics & numerical data*; D003625:Data Collection / Q000379:methods; D017723:Drug Utilization Review; D004812:Epidemiologic Methods; D006801:Humans; D009426:Netherlands / Q000453:epidemiology