title: Children are not goldfish--mark/recapture techniques and their application to injury data.
abstract: OBJECTIVE
  Mark/recapture (or capture-recapture) is a simple technique commonly applied to estimate the hypothetical total (including undercount) in a register composed of cases from two or more independent and separately incomplete case lists. This paper seeks to illustrate serious drawbacks in the use of the mark/recapture technique when applied to injuries.
  
  
  METHODS
  Northumbrian children under 15 years of age who were seriously injured in motor vehicle accidents (MVAs) over a five year period ascertained from two data sources: police reports and hospital inpatient records.
  
  
  METHODS
  Individuals (n) appearing in both police (S) and hospital (H) case lists are identified using various matching criteria. The separate and combined influence of age, sex, and casualty class (cyclist, passengers, pedestrians) on the probability of such matching is estimated using multivariate techniques. The hypothetical total incidence of child MVA victims (N) is calculated from N = (S x H)/n.
  
  
  RESULTS
  Estimates of the incidences of "serious" injuries in MVAs under various conditions of stratification and matching. The overall procedure is tested for conformity with accepted criteria for valid use of mark/recapture.
  
  
  RESULTS
  About one third of the 1009 police and 836 hospital records could be exactly matched. There were significant variations in matching proportions by class of accident (pedestrian v passenger v cyclist). This selective recapture or "heterogeneity" was not affected by sex, but was independently influenced by the age of the child. Further uncertainty was introduced when matching criteria were slightly relaxed. Estimates of the total population of children with serious injuries vary accordingly from 1729 to 2743. A number of plausible reasons why these two data sources might not be unbiased or mutually independent samples of the total target population are proposed as explanations for this heterogeneity.
  
  
  CONCLUSIONS
  This typical example of two sample mark/recapture estimation in an epidemiological setting can be shown to violate virtually all the requirements for valid use of the technique. Very little can be deduced accurately about the scale or characteristics of an unobserved group by the use of mark/recapture applied to two overlapping health event registers.
authors.affiliation: Department of Child Health, University of Newcastle upon Tyne, Gateshead, UK.
authors.forename: S N
authors.initials: SN
authors.lastname: Jarvis
authors.forename: P J
authors.initials: PJ
authors.lastname: Lowe
authors.forename: A
authors.initials: A
authors.lastname: Avery
authors.forename: S
authors.initials: S
authors.lastname: Levene
authors.forename: R M
authors.initials: RM
authors.lastname: Cormack
mesh_terms: D000063:Accidents, Traffic / Q000706:statistics & numerical data*; D000293:Adolescent; D017677:Age Distribution; D015982:Bias; D002648:Child; D002675:Child, Preschool; D003627:Data Interpretation, Statistical; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D015994:Incidence; D015601:Injury Severity Score; D008297:Male; D009049:Motorcycles; D015999:Multivariate Analysis; D011237:Predictive Value of Tests; D011336:Probability; D012042:Registries; D012307:Risk Factors; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D016019:Survival Analysis; D006113:United Kingdom / Q000453:epidemiology; D014947:Wounds and Injuries / Q000145:classification / Q000453:epidemiology*