Synthetic estimators in IrelandSynthetic estimators in Ireland

Anthony StainesAnthony StainesDCUDCU

What are synthetic estimators?What are synthetic estimators?

Estimates of something you haven't gotEstimates of something you haven't got Typically estimates for a small area of Typically estimates for a small area of

somethingsomething Making maximum use of what you haveMaking maximum use of what you have

ExampleExample

Lung cancer riskLung cancer risk Smoking is a key explanationSmoking is a key explanation Suppose you want to study the Suppose you want to study the

geography of lung cancergeography of lung cancer

What you haveWhat you have

Smoking data from a national survey by Smoking data from a national survey by age and sexage and sex

Small area level data on population and Small area level data on population and cancer incidence by age and sexcancer incidence by age and sex

What you can do at onceWhat you can do at once

Estimate prevalence for small areas Estimate prevalence for small areas included in the studyincluded in the study

Using the sample in the studyUsing the sample in the study

What's wrong with this?What's wrong with this?

The areas you need may not be includedThe areas you need may not be included The estimates will be very impreciseThe estimates will be very imprecise

You can do betterYou can do better

In some obvious waysIn some obvious ways And some not so obviousAnd some not so obvious

What you assumeWhat you assume

National age and sex specific rates apply National age and sex specific rates apply in each small areain each small area

And soAnd so

From these you calculate small area From these you calculate small area specific prevalence estimatesspecific prevalence estimates

This is indirect standardisationThis is indirect standardisation Can be done smarterCan be done smarter

requiring aggregation properties to holdrequiring aggregation properties to hold Adding in area level covariates (urban/rural Adding in area level covariates (urban/rural

etc.) etc.)

Can you do better?Can you do better?

YesYes

How?How?

Model based estimatorsModel based estimators

These have a long historyThese have a long history Many diverse applicationsMany diverse applications Combine survey data and some kind of Combine survey data and some kind of

'census data''census data' 'Census data' is that available for every 'Census data' is that available for every

area of interestarea of interest

RoughlyRoughly

Use the survey data to estimate Use the survey data to estimate relationships relationships

at the relevant levelat the relevant level between survey covariates between survey covariates and the census dataand the census data

ThenThen

Assume the same relationship applies in Assume the same relationship applies in the other areasthe other areas

IssuesIssues

Modelling can be hardModelling can be hard Remember these are predictive models, not Remember these are predictive models, not

explanatory modelsexplanatory models Data not easy to get at the right small Data not easy to get at the right small

area levelarea level

ModelsModels

models using individual level covariates models using individual level covariates onlyonly

models using area level covariates onlymodels using area level covariates only models combining individual and area-models combining individual and area-

level covariateslevel covariates

LimitsLimits

Available dataAvailable data ConfidentialityConfidentiality Complexity of methods, esp. multi-level Complexity of methods, esp. multi-level

methodsmethods ValidationValidation

Spatial data limitsSpatial data limits

Have to be able to link survey and census Have to be able to link survey and census to the same set of small areasto the same set of small areas

Given the primitive systems in the UK and Given the primitive systems in the UK and the nearly non-existent systems in the the nearly non-existent systems in the Republic this is a lot of workRepublic this is a lot of work

Errors here will lead to biassed estimatesErrors here will lead to biassed estimates

ConfidentialityConfidentiality

Need to respect confidentiality of survey Need to respect confidentiality of survey respondentsrespondents

May limit the data available for these May limit the data available for these purposespurposes

May need to design survey and survey May need to design survey and survey consent process carefully to get good consent process carefully to get good estimatesestimates

ModellingModelling

Can become very complexCan become very complex Clustered survey designsClustered survey designs Survey weightsSurvey weights Variable selectionVariable selection Model diagnosticsModel diagnostics

What and where to modelWhat and where to model

Data may exist at many different geographiesData may exist at many different geographies Multi-level models with individual, household, Multi-level models with individual, household,

local and regional effects can be consideredlocal and regional effects can be considered GIS might be very useful here for data GIS might be very useful here for data

handlinghandling Not advisable to aggregate covariates at Not advisable to aggregate covariates at

different spatial levelsdifferent spatial levels This is just making a bad embedded synthetic This is just making a bad embedded synthetic

estimatorestimator

ValidationValidation

Not easy to do, but essentialNot easy to do, but essential How do you validate your synthetic How do you validate your synthetic

estimates?estimates? Cross-validation?Cross-validation? Another survey?Another survey? ??

OptionsOptions

How aboutHow about Health Atlas Ireland?Health Atlas Ireland? This is a system built for HSE, (led by This is a system built for HSE, (led by

Howard Johnson) to plan health servicesHoward Johnson) to plan health services It already hasIt already has

MapsMaps CensusCensus HIPEHIPE Mortality dataMortality data

Census output optionsCensus output options

Recently they have developed a very Recently they have developed a very flexible census output systemflexible census output system

Uses census data at ED levelUses census data at ED level Locations of housesLocations of houses Assumes that all the houses in a DED are Assumes that all the houses in a DED are

exchangeableexchangeable

Census output optionsCensus output options

Allocates census data to any given areaAllocates census data to any given area Directly weighted by using the number of Directly weighted by using the number of

households and the ED composition of the households and the ED composition of the desired areadesired area

Futures?Futures?

Modern design of surveysModern design of surveys Could readily be extended to do SA from Could readily be extended to do SA from

almost any survey data where the almost any survey data where the necessary geographical data have bene necessary geographical data have bene collectedcollected

Greatly improves value for money of large Greatly improves value for money of large scale surveysscale surveys