Randomised Controlled Trial: The Effect of Asking for a Pledge on Charitable Donations

The randomised controlled trial is a suitable method to test whether or not an intervention is effective. Randomised controlled trials are often used in health research, but are currently much less common in the social sciences. In this case study, I explain how to design and undertake a randomised controlled trial, illustrated by a recent social science example, in which I tested different ways of asking people to donate a book to charity: asking for a pledge and promising publicity. I concentrate on the research design and introduce the importance of writing a pre-specified protocol. I explain the elements to include in the protocol and discuss the challenges this presents, using the book collection experiment as an example. I briefly introduce the importance of prior feasibility work before any trial and finish by suggesting, from my experience, the pros and cons of using randomised controlled trials as a research method.