Time is an important aspect of health economic evaluation, as the timing and duration of clinical events, healthcare interventions and their consequences all affect estimated costs and effects. These issues should be reflected in the design of health economic models. This article considers three important aspects of time in modelling: (1) which cohorts to simulate and how far into the future to extend the analysis; (2) the simulation of time, including the difference between discrete-time and continuous-time models, cycle lengths, and converting rates and probabilities; and (3) discounting future costs and effects to their present values. We provide a methodological overview of these issues and make recommendations to help inform both the conduct of cost-effectiveness analyses and the interpretation of their results. For choosing which cohorts to simulate and how many, we suggest analysts carefully assess potential reasons for variation in cost effectiveness between cohorts and the feasibility of subgroup-specific recommendations. For the simulation of time, we recommend using short cycles or continuous-time models to avoid biases and the need for half-cycle corrections, and provide advice on the correct conversion of transition probabilities in state transition models. Finally, for discounting, analysts should not only follow current guidance and report how discounting was conducted, especially in the case of differential discounting, but also seek to develop an understanding of its rationale. Our overall recommendations are that analysts explicitly state and justify their modelling choices regarding time and consider how alternative choices may impact on results.

Lifetime risk of developing colorectal cancer is 5%, and 5-year survival at early stage is 92%. Individuals with precancerous lesions removed at primary screening are typically recommended surveillance colonoscopy. Because greater benefits are anticipated for those with higher risk of colorectal cancer, scope for risk-specific surveillance recommendations exists. This review assesses published cost-effectiveness estimates of postpolypectomy surveillance to consider the potential for personalized recommendations by risk group. Meta-analyses of incidence of advanced neoplasia postpolypectomy for low-risk cases were comparable to those without adenoma, with both rates under the lifetime risk of 5%. This group may not benefit from intensive surveillance, which risks unnecessary harm and inefficient use of often scarce colonoscopy capacity. Therefore, greater personalization through deintensified strategies for low-risk individuals could be beneficial. The potential for noninvasive testing, such as fecal immunochemical tests, combined with primary prevention or chemoprevention may reserve colonoscopy for targeted use in personalized risk-stratified surveillance. This review appraised evidence supporting a program of personalized surveillance in patients with colorectal adenoma according to risk group and compared the effectiveness of surveillance colonoscopy with alternative prevention strategies. It assessed trade-offs among costs, benefits, and adverse effects that must be considered in a decision to adopt or reject personalized surveillance.

Background Low- and middle-income countries (LMICs) face a number of challenges in implementing cervical cancer prevention programmes that do not apply in high-income countries. Objective This review assessed how context-specific challenges of implementing cervical cancer prevention strategies in LMICs were accounted for in existing cost-effectiveness analysis (CEA) models of human papillomavirus (HPV) vaccination. Methods The databases of MEDLINE, EMBASE, NHS Economic Evaluation Database, EconLit, Web of Science, and the Center for the Evaluation of Value and Risk in Health (CEA) Registry were searched for studies published from 2006 to 2015. A descriptive, narrative, and interpretative synthesis of data was undertaken. Results Of the 33 studies included in the review, the majority acknowledged cost per vaccinated girl (CVG) (26 studies) and vaccine coverage rate (21 studies) as particular challenges for LMICs, while nine studies identified screening coverage rate as a challenge. Most of the studies estimated CVG as a composite of different cost items. However, the basis for the items within this composite cost was unclear. The majority used an assumption rather than an observed rate to represent screening and vaccination coverage rates. CVG, vaccine coverage and screening coverage were shown by some studies through sensitivity analyses to reverse the conclusions regarding cost-effectiveness, thereby significantly affecting policy recommendations. Conclusions While many studies recognized aspects of the particular challenges of HPV vaccination in LMICs, greater efforts need to be made in adapting models to account for these challenges. These include adapting costings of HPV vaccine delivery from other countries, learning from the outcomes of cervical cancer screening programmes in the same geographical region, and taking into account the country’s previous experience with other vaccination programmes.