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1.  The Relative Performance of Targeted Maximum Likelihood Estimators 
There is an active debate in the literature on censored data about the relative performance of model based maximum likelihood estimators, IPCW-estimators, and a variety of double robust semiparametric efficient estimators. Kang and Schafer (2007) demonstrate the fragility of double robust and IPCW-estimators in a simulation study with positivity violations. They focus on a simple missing data problem with covariates where one desires to estimate the mean of an outcome that is subject to missingness. Responses by Robins, et al. (2007), Tsiatis and Davidian (2007), Tan (2007) and Ridgeway and McCaffrey (2007) further explore the challenges faced by double robust estimators and offer suggestions for improving their stability. In this article, we join the debate by presenting targeted maximum likelihood estimators (TMLEs). We demonstrate that TMLEs that guarantee that the parametric submodel employed by the TMLE procedure respects the global bounds on the continuous outcomes, are especially suitable for dealing with positivity violations because in addition to being double robust and semiparametric efficient, they are substitution estimators. We demonstrate the practical performance of TMLEs relative to other estimators in the simulations designed by Kang and Schafer (2007) and in modified simulations with even greater estimation challenges.
PMCID: PMC3173607  PMID: 21931570
censored data; collaborative double robustness; collaborative targeted maximum likelihood estimation; double robust; estimator selection; inverse probability of censoring weighting; locally efficient estimation; maximum likelihood estimation; semiparametric model; targeted maximum likelihood estimation; targeted minimum loss based estimation; targeted nuisance parameter estimator selection
2.  Evaluating Health Care Programs by Combining Cost with Quality of Life Measures: A Case Study Comparing Capitation and Fee for Service 
Health Services Research  2008;43(4):1204-1222.
To demonstrate cost-effectiveness analysis (CEA) for evaluating different reimbursement models.
Data Sources/Study Setting
The CEA used an observational study comparing fee for service (FFS) versus capitation for Medicaid cases with severe mental illness (n =522). Under capitation, services were provided either directly (direct capitation [DC]) by not-for-profit community mental health centers (CMHC), or in a joint venture between CMHCs and a for-profit managed behavioral health organization (MBHO).
Study Design
A nonparametric matching method (genetic matching) was used to identify those cases that minimized baseline differences across the groups. Quality-adjusted life years (QALYs) were reported for each group. Incremental QALYs were valued at different thresholds for a QALY gained, and combined with cost estimates to plot cost-effectiveness acceptability curves.
Principal Findings
QALYs were similar across reimbursement models. Compared with FFS, the MBHO model had incremental costs of −$1,991 and the probability that this model was cost-effective exceeded 0.90. The DC model had incremental costs of $4,694; the probability that this model was cost-effective compared with FFS was <0.10.
A capitation model with a for-profit element was more cost-effective for Medicaid patients with severe mental illness than not-for-profit capitation or FFS models.
PMCID: PMC2517267  PMID: 18355261
Cost-effectiveness analysis; managed care organizations; QALY
3.  Cemented, cementless, and hybrid prostheses for total hip replacement: cost effectiveness analysis 
Objective To compare the cost effectiveness of the three most commonly chosen types of prosthesis for total hip replacement.
Design Lifetime cost effectiveness model with parameters estimated from individual patient data obtained from three large national databases.
Setting English National Health Service.
Participants Adults aged 55 to 84 undergoing primary total hip replacement for osteoarthritis.
Interventions Total hip replacement using either cemented, cementless, or hybrid prostheses.
Main outcome measures Cost (£), quality of life (EQ-5D-3L, where 0 represents death and 1 perfect health), quality adjusted life years (QALYs), incremental cost effectiveness ratios, and the probability that each prosthesis type is the most cost effective at alternative thresholds of willingness to pay for a QALY gain.
Results Lifetime costs were generally lowest with cemented prostheses, and postoperative quality of life and lifetime QALYs were highest with hybrid prostheses. For example, in women aged 70 mean costs were £6900 ($11 000; €8200) for cemented prostheses, £7800 for cementless prostheses, and £7500 for hybrid prostheses; mean postoperative EQ-5D scores were 0.78, 0.80, and 0.81, and the corresponding lifetime QALYs were 9.0, 9.2, and 9.3 years. The incremental cost per QALY for hybrid compared with cemented prostheses was £2500. If the threshold willingness to pay for a QALY gain exceeded £10 000, the probability that hybrid prostheses were most cost effective was about 70%. Hybrid prostheses have the highest probability of being the most cost effective in all subgroups, except in women aged 80, where cemented prostheses were most cost effective.
Conclusions Cemented prostheses were the least costly type for total hip replacement, but for most patient groups hybrid prostheses were the most cost effective. Cementless prostheses did not provide sufficient improvement in health outcomes to justify their additional costs.
PMCID: PMC3583598  PMID: 23447338

Results 1-3 (3)