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7/14/2003(c) 2003 Strategic Matching, Inc.1 29 th International Traffic Records Forum Using Multiple Imputation to Resolve Missing Data Issues
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7/14/2003(c) 2003 Strategic Matching, Inc.2 1. Imputation Methodology Mike McGlincy: Multiple imputation methodology and its appropriateness for highway safety missing data
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7/14/2003(c) 2003 Strategic Matching, Inc.3 2. The Number of Links Mike Allen: Estimating the true number of records that should link when imputing missing links
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7/14/2003(c) 2003 Strategic Matching, Inc.4 3. Sensitivity Analysis Jenny Qin: Performing sensitivity analyses of imputed missing values
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7/14/2003(c) 2003 Strategic Matching, Inc.5 4. Presenting Imputed Results Ted Donnelly: How to inspire confidence in the audience when presenting results based on imputed data
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7/14/2003(c) 2003 Strategic Matching, Inc.6 Research Question What is the effect of helmet use on inpatient charges for motorcycle riders discharged alive?
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7/14/2003(c) 2003 Strategic Matching, Inc.7 Traditional Linkage & Analysis Prepare crash and inpatient data Find high probability links Analyze complete cases
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7/14/2003(c) 2003 Strategic Matching, Inc.8 Prepare Data
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7/14/2003(c) 2003 Strategic Matching, Inc.9 Find High Probability Links
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7/14/2003(c) 2003 Strategic Matching, Inc.10 Linkage Results 527 high probability linked record pairs (44% of 1,200 estimated total). 56 motorcycle inpatients links, 19 with complete data.
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7/14/2003(c) 2003 Strategic Matching, Inc.11 Regression Analysis The REG Procedure © 2001 The SAS Institute, Inc. Model Information Data SetWORK.MC90 Model CHARGES = HELMET By Out Est Data SetWORK.OUTREG
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7/14/2003(c) 2003 Strategic Matching, Inc.12 Analysis Results Regression analysis of 19 complete cases (34% of high probability links) Estimated Effect = -$8,746
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7/14/2003(c) 2003 Strategic Matching, Inc.13 Missing Data Issues High levels of missing links and missing values introduce uncertainty about true effect of helmet use. Complete case analysis is probably not representative of all motorcycle inpatients.
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7/14/2003(c) 2003 Strategic Matching, Inc.14 A Key to Better Results Solve missing data problems with a multiple imputation strategy
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7/14/2003(c) 2003 Strategic Matching, Inc.15 Multiple Imputation 1.Make several estimates for all missing links and missing values (imputations). 2.Do a separate analysis for each complete imputation. 3.Average the separate results.
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7/14/2003(c) 2003 Strategic Matching, Inc.16 Valid Imputations For valid (“proper”) imputations, missing links and values must be chosen according to a posterior probability distribution determined by Bayesian analysis.
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7/14/2003(c) 2003 Strategic Matching, Inc.17 Bayesian Analysis 1.Create a joint probability distribution (a model) relating all observable and unobservable quantities in the problem. 2.Determine parameters in the model by taking into account all observed data.
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7/14/2003(c) 2003 Strategic Matching, Inc.18 A Key to Better Linkage Use CODES2000 or LinkSolv software for multiple imputation of missing links
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7/14/2003(c) 2003 Strategic Matching, Inc.19 Impute Missing Links
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7/14/2003(c) 2003 Strategic Matching, Inc.20 Linkage Results 1,296 imputed linked record pairs (vs. 527 high probability links and 1,200 estimated total links). 72 motorcycle inpatients links (vs. 56 high probability links).
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7/14/2003(c) 2003 Strategic Matching, Inc.21 A Key to Better Analysis Use SAS MI, NORM, or S+ software for multiple imputation of missing values
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7/14/2003(c) 2003 Strategic Matching, Inc.22 Impute Missing Values The MI Procedure © 2001 The SAS Institute, Inc. Model Information Data SetWORK.MCMINORM MethodMCMC Multiple Imputation ChainSingle Chain Initial Estimates for MCMCEM Posterior Mode StartStarting Value PriorJeffreys Number of Imputations5 Number of Burn-in Iterations200 Number of Iterations100 Seed for random number generator37851
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7/14/2003(c) 2003 Strategic Matching, Inc.23 Regression Analysis The REG Procedure © 2001 The SAS Institute, Inc. Model Information Data SetWORK.MCMI25 Model CHARGES = HELMET By_IMPUTATION_ Out Est Data SetWORK.OUTREG
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7/14/2003(c) 2003 Strategic Matching, Inc.24 Multiple Helmet Effects
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7/14/2003(c) 2003 Strategic Matching, Inc.25 Combined Helmet Effect The MIANALYZE Procedure © 2001 The SAS Institute, Inc. Model Information Data SetWORK.OUTREG Number of Imputations25
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7/14/2003(c) 2003 Strategic Matching, Inc.26 Helmet Effect Comparison Traditional analysis: Helmet Effect = -$8,746 Multiple imputation analysis: Helmet Effect = -$2,150
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7/14/2003(c) 2003 Strategic Matching, Inc.27 Highway Safety Imputations FARS missing links: Crash to Death FARS missing values: BAC CODES missing links: Crash to Med CODES missing values: Belts, DUI…
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