15.2.3  Specifying types of health economics studies and the scope of the economics component of a review

A critical review of health economics studies should specify at the outset which types of studies will be considered for inclusion (see also Section 15.1.2). This decision is driven primarily by the economic questions or objectives that have been formulated and the measures of resource use, costs and cost-effectiveness included as target outcome measures.

 

This decision should be made in consultation with a health economist, since it is not necessarily a straightforward exercise to map the analytic pathways between different forms of economic questions, ‘economic’ outcome measures and different types of health economics studies. For example, if a cost-effectiveness analysis includes reporting of results from all interim stages of analysis alongside final results, it may be possible to extract outcome data relating to measures of resource use, costs and cost-effectiveness; however if only final results are reported, it may only be possible to extract outcome data relating to measures of cost-effectiveness.

 

The types of health economics studies to be considered for inclusion in the review should be stated in the ‘Types of studies’ part of the ‘Criteria for considering studies for this review’ section. An illustrative statement featuring the full range of types of economics studies is as follows:

 

Types of studies

The following types of studies will be considered for inclusion in the critical review of health economics studies:

Full economic evaluation studies (i.e. cost-effectiveness analyses, cost-utility analyses, cost-benefit analyses) of [intervention(s) versus comparator(s)]; partial economic evaluations (i.e. cost analyses, cost-description studies, cost-outcome descriptions) of [intervention(s) and comparator(s)]; and randomized trials reporting more limited information, such as estimates of resource use or costs associated with [intervention(s) and comparator(s)].

 

A final key methodological decision when planning a critical review of health economics studies is to set out the scope of this element of the review process. There are at least three options for the scope of a critical review of health economics studies:

  1. Consider only relevant health economics studies conducted alongside effectiveness studies that meet eligibility criteria for the effectiveness component of the review;

  2. Consider relevant health economics studies conducted alongside, and also those based upon data sourced from effectiveness studies that meet eligibility criteria for the effectiveness component of the review;

  3. Consider all relevant health economics studies, whether or not conducted alongside, or based upon, effectiveness studies that meet eligibility criteria for the effectiveness component of the review.

 

The first option might typically allow only health economics studies conducted alongside high quality randomized trials to be considered for inclusion in the economics component of the review. The second option would additionally allow for consideration of economic modelling studies based on a meta-analysis of data from high quality randomized trials. A good example of a review of health economic models is the review of screening for abdominal aortic aneurysm conducted by Campbell and colleagues (Campbell 2007). The third option is clearly a more inclusive one that allows for consideration of all relevant health economics studies, including those based upon observational studies or analysis of large administrative databases, or regression-based cost and resource use analyses, for example.

 

Little is known about the impact of including these different types of health economics studies upon the results of a critical review. However, it is plausible that this type of decision regarding ‘scope’ at least has the potential impact on results, since different options may involve consideration of different sets of studies (see also Section 15.5.2). Also, where a review includes both economic evaluations based on single studies (e.g. randomized trials) and model-based economic evaluations, it may be optimal to consider each of these categories of studies separately, in order to retain comparability amongst studies.

 

In practice, a majority of current Cochrane reviews that set out to incorporate coverage of evidence from health economics studies restrict this coverage to economic studies conducted alongside effectiveness studies meeting eligibility criteria for the effectiveness component of the review (i.e. the first option), but do not state this explicitly (Shemilt 2007). Since the decision regarding scope has the potential to exclude some health economics studies without any recourse to critical appraisal of their methodological quality, the result of this decision should be stated in the ‘Types of studies’ part of the ‘Criteria for considering studies for this review’ section of a review, alongside details of the types of economic studies to be considered for inclusion, for example by appending “The review will consider only health economics studies conducted alongside effectiveness studies included in the effectiveness component of the review” to the illustrative statement above.