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design of the sampling frame of the 2008 French survey on disability and health INSEE Loic Midy. Problem to solve: How can we get a high number of people with disability in the sample of our survey? Our solution: we do a two phase survey:
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design of the sampling frame of the 2008 French survey on disability and healthINSEE Loic Midy
Problem to solve: How can we get a high number of people with disability in the sample of our survey? • Our solution: we do a two phase survey: • Step 1: we did in 2007 a short survey called VQS on 140 000 households • Step 2: we classify VQS respondants into stratums of assumed severity of disability • Step 3 : the sample of the disability survey (size 39 000) is a stratified sampling on those stratums
This methodology will be of good quality only if all the 3 steps have themselves a good quality. This raises 3 issues tackled in this presentation • Issue 1 (linked to step 1): how should we design the short set of questions of VQS in order to detect people with disability? • Issue 2 (linked to step 2): how should we do the classification of VQS respondants into stratums of severity of disability? • Issue 3 (linked to step 3):what rules should the stratified sampling of the disability survey follow?
Issue 1: design of VQSquestions Global philosophy: disability\handicap is a multi dimensionnal issue. Backed by a study of the 1999 VQS data on the people aged 16 or more: • 2,4% persons declared a global limitation for 6 months or more but not a single functionnal limitations (7 questions). • 13,3% persons declared a least one functionnal limitation but no global limitation for 6 months or more. • 14% of the persons who have an official recognition of a disability\ handicap don’t think they have a disability\ handicap !!!
Issue 1 (2) Dimensions included in the 2007 VQS • Questions on health (mini module 1 and 2) • Question on limitation (mini module 3) • Questions on functionnal limitations • Questions on help (human, technical, and housing adaptations) • Question on self perception of handicap • Question on official recognition of handicap
Issue 1 (3) the intellectual and psychical handicap were not well detected with the 1999 VQS questions: • 48% of HID respondants who declared that they often put themselves in danger answered NO to all 1999 VQS questions. • 63% of HID respondants who declared that people often reproached them to be to agressive or to impulsive answered NO to all 1999 VQS questions.
Issue 1 (4) => we added 4 questions to detect those handicap. Those 4 questions where asked in another survey on adults asking an official recognition of handicap where the real impairment is available (coded by a general practitionner using the medical files)
Issue 2 We used 2 methods to classify VQS respondant: • One is based on a score • The second is a mixed classification
Issue 2: score Principle: • A note is assigned to each answer. Ex: question How is your health in general • Answer very bad=>5 points • Answer bad=>3 points • Final score for a person=(sum of note)\ (maximum sum of note)*100 => partial non response taken into account • Allocation of each person to a stratum according to his score (ex: if score>80 => stratum 4). • Arbitrary threshold • OR hierachical classification on a sample of persons on variable final score
Issue 2 (2) How can we assign a weight to each answer? In 1999 we had a VQS survey and then a disability survey called HID. We detect the VQS 1999 questions explaining the best one HID variable by a logistic regression => Gives an idea of the most important VQS questions BUT not perfect nor complete because VQS 1999 and VQS 2007 are not all the same (questions added, deleted, reformulated)
Issue 2 : mixed classification The steps are: • Basic imputation on missing data : non response => imputation answer NO. • Analysis of multiples correspondancies (ACM) • Classification (mobile centers méthod: SAS: FASTCLUS) on the firsts axes of the ACM=> 10 000 clusters • Hierarchical classification (SAS: CLUSTER) on the 10 000 clusters
Issue 3 • what rules should the stratified sampling of the disability survey follow? • We have 4 stratums of severity of handicap from 1 (no handicap at all) to 4 (important handicap). • We sample 100% of people in stratum 4. The main question is which percentage of people should we sample in stratum 1?
Issue 3 (2) We should estimation confidence interval on variable of interest to answer BUT is this case the calculus are very difficult=> study of the dispersion of the weight.