Methods: The PubMed database was searched to identify relevant model-based CEAs of cervical screening programmes using HPV testing either as a primary test or as triage tool for borderline primary results. The relevant CEAs were then carefully appraised for their quality of analyses, reporting and interpretation of results. Specific examples of modelling shortcomings were selected to be presented as illustrations of what to avoid when estimating the cost-effectiveness of HPV-based screening.
Results: The literature search identified 759 titles and abstracts of interest, of which 29 were relevant CEAs. Regarding basic errors, 11 of the 29 studies calculated or reported the incremental cost-effectiveness ratios (ICERs) of the efficient screening strategies either partly or completely incorrectly. Ten studies failed to fully report cost and effects estimates, instead they either simply reported ICERs or depicted a cost-effectiveness plane. Regarding more fundamental errors, 23 studies failed to include sufficient alternative screening intervals to serve as relevant comparators against which to meaningfully estimate the incremental cost-effectiveness of screening: effectively leading to average cost-effectiveness ratios being mistakenly identified as ICERs, which biases estimates downwards. Finally, none of the 29 studies clearly distinguished the change in costs and effects of switching to HPV testing for a given screening frequency from the incremental cost-effectiveness of that screening frequency using HPV testing relative to the next efficient comparator, which matters as the cost-effectiveness ratios of these two comparisons can be quite different.
Conclusions: Specifying the model is typically the most difficult part of a model-based CEA, whereas simulating relevant strategies is relatively easy once the model is built. Similarly, once the results have been generated, the correct presentation and interpretation of them is relatively straightforward. However, this analysis shows that these easier aspects of CEA are being performed poorly in the HPV screening literature. Simple steps could be taken to gather the low hanging fruit of the inclusion of relevant comparators and improved reporting and interpretation of results. Such improvements would provide decision makers with much more useful and reliable evidence of what screening strategies are optimal.
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