Objectives: We describe recent methodological concerns and advances that properly exploit randomisation even while examining relationships among post-randomisation measures and then consider some of the implications these have for measurement protocols and design.
Methods: Using the Pre-School Autism Communication Trial (PACT) as an illustrative vehicle we describe the combination of trajectory models that characterise the joint development of parent and child interaction during progress of the trial and counterfactual thinking that helps characterise the impact of treatment in a way that continues to exploit randomisation. We consider how these models can be extended to consider the transmission or disattenuation of effects to final outcome, and the appropriate ways in which we should assess the extent to which effects are transmitted along/mediated in the hypothesized manner. In so doing we highlight some of the implicit but implausible assumptions commonly made in the analysis of mediation.
Results: Trial data is complete but due to a pre-publication embargo on the study findings we are unable to summarise the empirical findings in this abstract. However all data and analysis will be available for presentation at the IMFAR meeting.
Conclusions: Treatment trials can and should be viewed and designed both as tests of proposed treatments and as research tools with which to explore and refine the therapeutic pathway.