I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES Capture-recapture methodology for estimating hard-to-reach populations: Estimating the number of usual residents in the Netherlands 2010 S.C. Gerritse Statistics Netherlands
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES S USANNA G ERRITSE Bachelor Clinical Psychology (University of Amsterdam) Research Master Psychology, major in Methodology (University of Amsterdam) PhD candidate (Utrecht University, Collaboration with Statistics Netherlands). "Capture-recapture methodology on register data for quality report for the Census " Extracuricular: PhD Network Netherlands
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES P H D P ROJECT Prof. Dr. Bart F. M. Bakker Register and Administrative data Prof. Dr. Peter G. M. van der Heijden . Statistics My PhD: Capture-recapture methodology Sensitivity analyses on assumptions methodology Application to quality report of Census 2011
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES G OAL What are the number of usual residents in the Netherlands? Residing in the Netherlands for longer than 12 months Why important to this Summer school? Hard-to-reach sub populations Solution: Census Quality Census?
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C ENSUS Eurostat: every ten years each European country has to conduct a Census Conducted by National Statistical Institute (NSI’s). Complete overview population Provides information to develop policies, plan and run public services, and allocate funding. Why do we need this?: How many homeless people are there? → Do we need more shelters? How many people or different ethnicities do we have? → Evaluating equal opportunities policies How many people live in the capital city? → Do we need to build more (student-)housing?
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C ENSUS How can we conduct a Census? Traditional Census Enumerate every individual Either internet form or door-to-door poll officers Advantages: Enumerate almost everyone Disadvantages: Costly, a burden on the resident, non-response Countries: UK, Ireland, Portugal, Russia, Greece, etc. Rolling Census: Traditional Census spread out Enumerating different characteristics over multiple years Advantages: higher frequency of Census data Disadvantages: Costs, more burden France, US.
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C ENSUS
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C ENSUS Register based, administrative census. One or more registers Most important: Population register Advantages: Less costs, data already exists, no burden on the residents, higher frequency Disadvantages: Data are collected for other reasons. Finland, Norway, Sweden Integrated Census: Administrative data and enumeration Combination of Administrative data and additional survey’s All the advantages of admin data, plus extra information via survey Netherlands, Belgium, Germany, Poland, Spain, Italy, Israel.
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C ENSUS
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES H ARD - TO - REACH - POPULATIONS Dutch Census: Since 1995: Automated population registration system Most important: Population register based on data from municipalities (municipalities own the data) The Population Register is incomplete → Undercoverage Free movement and residence within EU Illegal immigrants Undercoverage PR What is the quality of the PR? How can we estimate the hard-to-reach population? → Capture-recapture estimation Note: Overcoverage.
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES O VERVIEW Overview: Capture-recapture methodology Outcomes my PhD Other methods to estimate hard-to-reach populations, examples in Europe
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C APTURE -R ECAPTURE Population size estimation technique Originated from animal estimation The Tundra Vole: In the ’Turfzakken’ polder, in 2009: On 10 different locations, in total 20 cages. Captured voles were noted and information collected. Some hair on their back was removed - Tag. A week later they repeated the process Three counts: Voles caught in the first sample Voles caught in the second sample Voles caught in both camples
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C APTURE - RECAPTURE
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C APTURE -R ECAPTURE Human estimation? Already existing administrative data Linking two (incomplete) registers PR, Dutch Population Register containing the registered population CSR, Crime Suspects register, Police register on suspects of known offenses Table: Expected values CSR PR 1 0 1 m 11 m 10 0 m 01 m 00
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES I NDEPENDENCE Under independence Loglineair model log m ij = λ + λ A i + λ B j where λ A 1 = λ B 1 = 0. Odds ratio m 00 m 11 m 10 m 01 = 1 Two ways to estimate m 00 : m 00 = exp (ˆ Poisson loglinear regression: ˆ λ ) Maximum likelihood estimate (mle): m 00 = ˆ m 10 ˆ m 01 = n 10 n 01 ˆ n 11 . ˆ m 11
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES E STIMATING THE VOLES Table: Population voles Sample 1 Sample 2 1 0 1 2 6 0 6 ? Odds ratio m 11 m 00 m 10 m 01 = 1 . ˆ m 10 ˆ m 01 m 00 . → n 10 n 01 = ˆ = ˆ m 00 . ˆ m 11 n 11 6 ∗ 6 = 18 . → 6 + 6 + 2 + 18 = 32 2
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES C APTURE - RECAPTURE
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES A SSUMPTIONS Assumptions Independence between registers Perfect linkage of individuals in registers No erroneous captures Heterogeneous inclusion probabilities Closed population Two issues: How do you meet the assumptions? Effect of violation on population size estimate? Literature? Sensitivity analyses
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES D ATA Compare two different nationality groups. Afghan, Iraqi, Iranian Need visum for the Netherlands Polish EU → free movement and residence Table: Observed values and estimate ˆ m 00 CSR CSR PR 1 0 PR 1 0 1 1,085 26,254 1 374 39,488 0 255 6,170.3 0 1,445 152,567.3 (a) Population of people with an (b) Population of people with a Polish Afghan, Iraqi and Iranian (AII) nationality residing in the Netherlands nationality residing in the in 2009 Netherlands in 2007
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES I NDEPENDENCE
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES P ERFECT L INKAGE
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES E RRONEOUS CAPTURES
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES I MPLIED COVERAGE Why is there such a difference between the nationality groups? Implied coverage Table: Observed counts mle ˆ m 00 HKS HKS GBA 1 0 GBA 1 0 1 1,085 26,254 1 374 39,488 0 255 6,170.3 0 1,445 152,567.3 (a) Afghan, Iraqi, Irani nationality in (b) Polish nationality in the Netherlands, the Netherlands, 2007 2009 Overlap between the registers Coverage of the PR, given the CSR. Low implied coverage → High estimation → Not robust High implied coverage → Low estimation → Robust.
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES M ETHOD What is the number of usual residents in the Netherlands? We used three registers. Population register - PR Crime Suspects Register (police) - CSR Employee Register - ER Important: Length of stay PR: Difference between Census date and date of registration However: present before date of registration? Assumption: Everyone registered in the PR has the intention to stay for 12 months ER - job lengths Assumption: Residence in NL during the time of the job Unemployed between jobs? CSR - ? Impute.
I NTRO C ENSUS C APTURE -R ECAPTURE A SSUMPTIONS U SUAL R ESIDENTS O THER M ETHODS AND PRACTICES U NDERCOVERAGE PR Three registers (PR, CSR, ER) Multiple covariates (Sex, Age, Usual Residence, and nationality group) Deterministic en probabilistic linkage Delete erroneous captures PR and ER: Census date CSR: Period of half a year Method: Impute missing values Predictive Mean Matching (PMM) multiple imputation Generalized Loglinear Modeling (GLM) - Poisson verdeling
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