OBJECTIVES

In 2003 the DPP published a within-trial 3 year cost-effectiveness analysis (CEA). The authors appear to have ignored missing data and used ACA, reporting QALYs using the QWB to measure patient utilities for placebo (PBO), lifestyle (LS), and metformin (MET). The main objective of this research is to estimate treatment utilities and QALYs using Multiple Imputation (MI) and compare these results with previous ACA findings.

METHODS

We had access to a 95% subset of the original data. We reproduced the original ACA results and then used MI to develop estimates for utilities and QALYs based on the QALY calculation method used in the original CEA. 5 imputed datasets were pooled into a single imputed dataset. The percentages of participants with at least one missing utility data for QWB for years 1, 2 and 3 were 36%, 10 % and 48%.

RESULTS

The yearly utility scores using the QWB originally reported in the DPP were [0.686, 0.675, 0.657], [0.687, 0.680, 0.673] and [0.703, 0.695, 0.692] for PBO, MET, and LS. The utility scores using MI were [0.685, 0.676, 0.669], [0.688, 0.683, 0.681] and [0.705, 0.694, 0.694].

QALYs using the QWB as originally calculated were 2.018, 2.040 and 2.090 for PBO, MET and LS. The MI QALYs were 2.030, 2.053 and 2.094. The incremental QALYs using the QWB as originally calculated were 0.072, 0.022 and 0.050 for LS versus PBO, MET versus PBO, and LS versus MET. The MI incremental QALYs were 0.064, 0.023 and 0.041.

CONCLUSIONS

The missing data and MI estimates in the DPP yielded different incremental QALYs compared to the ones reported in the original DPP study. Small differences in QALYs have been shown previously to be important in the DPP CEA conclusions. These differences may be important in their CEA implications, a subject for future research.