Let us now look at some of these threats before examining potential alternatives to RCTs.

The challenges of conducting successful RCTs

Successfully implementing RCTs is not an easy task, mainly due to technical challenges such as ensuring double-blinding, avoiding pseudo-random methods, addressing attrition and considering behavioural changes caused by the experiment itself such as Hawthorne and John Henry effects which may affect the results in positive as well as negative ways (as explained below). Furthermore, spill-over effects cannot be fully ruled out, and ethical and practical challenges need to be considered. We will now investigate some of these challenges in more depth and start with the key feature of RCTs, which is double-blinding.

Evaluation expert Michael Scriven, among others, stresses that double-blinding is one of the prerequisites for a robust RCT. Double-blinding implies that individuals participating in the RCT and researchers executing the RCT do not know who is receiving a particular treatment or not.