Statistical Aspects of Cost-Effectiveness Analysis of Vaccination for Alzheimer’s Disease
Date Issued
2011
Date
2011
Author(s)
Yang, Kuen-Cheh
Abstract
Background: Alzheimer’s disease (AD) is a degenerative chronic disease, also the most common form of dementia. Although some current medications may delay the progression, it is not possible cure for AD. In 1990s, studies on immunotherapy for AD have been published. Since then, more immunotherapies with a clinical trial design entered the different stages. However, no economic valuation for the cost-effectiveness of immunotherapy for AD was performed. Vaccination against AD is illustrated to this study. However, the censored data are a common feature in clinical trials. If we ignore the censored problem, bias of estimation would occur because the cost and efficacy still accumulate after censoring. Additionally, the complicated Markov model would be applied to different status of disease nature course. Finally, the relationships between costs and effectiveness are often ignored. Therefore, this thesis used the cost-effectiveness analysis of vaccination for Alzheimer’s disease as an example to illustrate the methods how to resolve above problems.
Methods: We used a Markov cost-effectiveness model to construct the nature course of AD. The micro-simulation was used to create a hypothetical cohort. The transition probabilities were extracted from previous Taiwanese studies. The treatment group is the participants with the uptake of vaccination and the control group is those without vaccination. The duration of follow-up is 6 years and each group consists of 1000 participants. First, the cost and effectiveness were measured without considering censoring data. Furthermore, they were measured by Direct (Lin) and Inverse probability weighting (IPW) to make allowance for censoring data. The outcome of interests included person years and quality-adjusted life year (QALY). Given the threshold of $10,000 of willingness-to-pay (WTP), we evaluate the probability of being cost-effectiveness for the treatment group by cost-effectiveness acceptability curve (CEAC).
Results: (1) Without considering censored data, probabilistic analysis showed ICER was $3000 per QALY (95% CI: $-12,000~$14,000); INB was $2,729 (95% CI: $-1,003~11,634). Given the threshold of $10,000 of WTP, the probability of being cost-effective for the treatment group versus the control was 88.4% in terms of QALY. (2) Considering censored data, the costs estimated by Direct (Lin) or IPW were higher than those without considering censored data. The ICER of mean survival time was $9,310 per person-year (90% CI: $4,402~$13,322) estimated by Direct (Lin) and $6,987 per person year (90% CI: $937~$11,646) estimated by IPW, respectively. The ICER of mean quality-adjusted survival time was $12,885 per QALY (90% CI: $5,808~ $19,132) and $8,955 per QALY (90% CI: $1,066~16319) by Direct (Lin) or IPW, respectively. The mean survival time and QALY for AD were not cost-effective given the threshold of $10,000 of WTP. Given the threshold of $10,000 of WTP, the probability of being cost-effective for the treatment group were 85% and 59% in terms of mean survival time and QALY, respectively, by IPW estimation. The corresponding figures were 60.5% and 24% in terms of mean survival time and QALY, respectively, by Direct (Lin) estimation.
Conclusions: By using Direct (Lin), IPW methods and Markov decision model, we demonstrated adjusting for censoring could adjust for censoring lead to downward estimation using an illustration of vaccination against AD.
Subjects
Censored data
cost effectiveness analysis
immunotherapy
SDGs
Type
thesis
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