Evaluating non-randomised intervention studies - NIHR Health ...

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Empirical evaluation of the ability of case-mix adjustment methodologies to control for selection biasTABLE 29 Comparison of methods of case-mix adjustment applied to results of concurrently controlled studies with results of RCTsresampled from eight regions within the ECSTPercentage of studies withstatistically significantAverageVariability of results results (p < 0.05)OR SD of log OR Ratio with RCT Benefit Harm TotalRCT 1.08 0.69 3 5 9Concurrently controlled studiesUnadjusted 1.08 0.69 1.01 3 6 9Stratification 1.09 0.74 1.08 3 6 9Logistic regressionFull model a 1.20 1.43 2.10 4 6 10Stepwise p r = 0.05 b 1.06 0.82 1.21 5 7 12Stepwise p r = 0.15 c 1.07 0.91 1.34 5 8 13Propensity scoreMatched d 1.05 0.87 1.27 2 6 8Stratified 1.06 0.82 1.20 5 3 8Regression 1.06 0.80 1.17 5 3 8a Full model includes eight covariates.b Mean number of covariates included: 1.90.c Mean number of covariates included: 3.06.d Mean number of patients matched: 40/80.1005020105Odds ratio210.50.20.10.050.020.01RCTs CCs LR(F) LR(5%) LR(15%) MH PS(M) PS(S) PS(R)FIGURE 16 Comparison of methods of case-mix adjustment applied to results of concurrently controlled studies resampled from 14regions within the IST. RCT: results from corresponding randomised controlled trials; CCs: unadjusted concurrent controls withoutadjustment, LR(F): adjustment using full logistic regression analysis; LR(5%): adjustment with stepwise logistic regression withp r = 0.05; LR(15%): adjustment with stepwise logistic regression with p r = 0.15; MH: adjustment by Mantel–Haenszel stratification;PS(M): adjustment by matching on propensity score; PS(S): adjustment by stratification on propensity score; PS(R): regressionadjustment based on propensity score.76
Health Technology Assessment 2003; Vol. 7: No. 27TABLE 30 Case-mix adjustment with bias caused by a known and measured single covariate [neurological deficit score (IST)]Percentage of studies withstatistically significantAverageVariability of results results (p < 0.05)OR SD of log OR Ratio with RCT Benefit Harm TotalRCT 0.91 0.33 7 2 9Studies where treatment is related to conditionUnadjusted 0.53 0.36 1.09 53 0 53Stratification 0.93 0.41 1.24 7 3 10Logistic regressionFull model a 0.89 0.55 1.67 8 3 11Stepwise p r = 0.05 b 0.87 0.51 1.55 12 3 15Stepwise p r = 0.15 c 0.88 0.52 1.58 10 3 13Propensity scoreMatched d 0.93 0.45 1.36 4 2 6Stratified 0.90 0.40 1.21 6 2 8Regression 0.92 0.39 1.18 5 2 7a Full model includes 10 covariates (including neurological deficit score).b Mean number of covariates included: 4.6.c Mean number of covariates included: 5.9.d Mean number of patients matched: 127 out of 200.TABLE 31 Case-mix adjustment with bias caused by a known but unmeasured single covariate [consciousness level (IST)]Percentage of studies withstatistically significantAverageVariability of results results (p < 0.05)OR SD of log OR Ratio with RCT Benefit Harm TotalRCT 0.91 0.33 7 2 9Studies where treatment is related to conditionUnadjusted 0.64 0.34 1.03 34 0 34Stratification 0.70 0.38 1.15 23 0 23Logistic regressionFull model a 0.71 0.48 1.45 17 1 18Stepwise p r = 0.05 b 0.69 0.43 1.30 21 1 22Stepwise p r = 0.15 c 0.69 0.44 1.33 20 1 21Propensity scoreMatched d 0.79 0.38 1.15 9 0 9Stratified 0.77 0.34 1.03 12 0 12Regression 0.78 0.34 1.03 11 0 11a Full model includes 10 covariates (excludes consciousness).b Mean number of covariates included: 4.0.c Mean number of covariates included: 5.3.d Mean number of patients matched: 134 out of 200.used as the variable for stratification. The bias wasappropriately adjusted for by all seven methods.Adjustments made by stratification gave resultsclosest to those of the RCTs.Adjusting for bias due to a known butunmeasured covariateTable 31 reports results of case-mix adjustment forthe bias in the IST trial introduced whentreatment allocation was linked to the level ofconsciousness at admission. However, in thissituation, the adjustments were made without thecovariate indicating level of consciousness beingincluded in the models. As before, stratificationwas undertaken using the neurological deficitscore, but the regression and propensity scoremodels were based on the remaining nine out of10 covariates.77© Queen’s Printer and Controller of HMSO 2003. All rights reserved.
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