Developing logic models for promising models

Where models are currently used on a small scale, they can be caught in the ‘evidence trap’: the numbers using them only enable small-scale, largely qualitative evaluations, which typically conclude that they are promising but ‘more research is needed’.

Some small-scale models already have sufficient evidence of outcomes and cost-effectiveness or savings to justify ambitious scale-up programmes. For others, a logic modelling approach would enable cases to be made for incremental investment based on testing the model’s outcomes against those which it claims will be delivered.

We recommend using Nesta’s Theory of Change approach to identify the model’s inputs, activities, assumptions and intended short- and longer-term outcomes and impacts for its target group(s). To make incremental investment in the model feasible, it is necessary to identify tangible reductions in, or avoidance of, costs to the system, as well as the outcomes most valued by the individuals and families using the service.

Savings could come from:

To develop a theory of change, you need to identify:

This will enable you to set targets for the initial phase of the programme, based on the new intervention achieving sufficient cost-reducing outcomes to balance its costs.

An investment plan will be needed which includes regular review of the level of investment so that decision-makers can respond to good and poor outcomes.

Poor outcomes should lead to the intervention being redesigned, reduced or discontinued.

Good outcomes should lead to increasing investment.

Unless transition funds or social investment has been identified, this will usually require consideration of which other parts of the system may need to see reduced investment.

Nesta’s Theory of Change model

Further information