Do randomised control trials offer a solution to 'low quality' transport research?
University of the West of England, Bristol.
This article responds to Graham-Rowe et al (2011), published in issue 45 of this journal, which categorised 77 evaluations of transport interventions into 5 levels of ‘quality’. This article focuses on Graham-Rowe et al’s treatment of randomised control trials (RCTs) and their recommendation, also made by others, that RCTs should be used ‘wherever possible’ in transport research. It analyses the RCTs reviewed by Graham-Rowe et al and draws on the methodological literature and literature on Voluntary Travel Behaviour Change to illustrate how claims about the advantages of RCTs, in establishing causality and avoiding bias, have been exaggerated. It proposes 8 criteria for the valid application of RCTs. These criteria limit the application of RCTs to small-scale and relatively simple transport questions. Using RCTs to address larger transport questions, or to quantify the contribution of separable elements of more complex interventions, risks generating misleading conclusions for policy and practice.
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