Currently there is almost no research in the area, so you would have to narrow it down using heuristics.
The Old Way
Last year, I somewhat informally narrowed down the options until I chose to run a study on handing out educational leaflets. The rough steps I followed were to:
The New Way
I have recently been thinking of a different system that may work better than this. It basically boils down to using the heuristic of neglectedness a lot more, and would look more like the following:
It is important to look at the pros and cons of a method, and here are some of the potential flaws with this system:
That being said it seems like a possibly interesting way of determining what specific interventions would be worth running a randomized controlled trial on in an area that has very limited evidence so far.