Table 2 Types of study designs well suited to providing particular types of information about options

Benefits

(i.e. positive effects)

Randomised controlled trials

• Experimental study in which individuals are randomly allocated to be exposed to different policy and programme options (e.g. using the toss of a coin or a list of random numbers generated by a computer)

Interrupted time series

• Study using observations at multiple time points before and after a policy or programme is introduced (this is referred to as an 'interruption'). The design attempts to detect whether a policy or programme has had an effect significantly greater than any underlying trend over time

Controlled before/after studies*

• Study in which observations are made before and after the implementation of a policy or programme, both in a group that is exposed to the policy or programme and in a control group that is not. Data collection is done concurrently in the two groups

Potential harms (i.e. negative effects)

Effectiveness studies (see above)

Observational studies

• Study in which observations are made about those exposed to a policy or programme. Data could be drawn from administrative databases, community surveys or other sources

Costs and cost-effectiveness

Cost-effectiveness studies

• Study in which the relative expenditures (costs) and outcomes (effects) of two or more courses of action are compared

Key elements of the option (how and why it works)

Qualitative studies carried out alongside a study of effects (i.e. process evaluations)

• Study conducted in natural settings and usually aimed at interpreting or making sense of phenomena in terms of the meanings people bring to them. Typically, narrative data are collected from individuals or groups of 'informants' (through interviews, focus groups, participant observation) or from documents. These are then interpreted by researchers

Views and experiences of stakeholders

Qualitative studies

• See above

Observational studies

• See above