Many of these findings and observations have been made before — often in an off-hand manner, without particularly strong empirical support. And this brings us to our final point: there is still a lack of good empirical studies that provide more rigorous
answers to ‘how to’ questions. When we first came to the subject 20 years ago, this was our initial insight [23], which we followed up with a number of empirical studies that, we felt, were as important for showing how one might research Delphi processes as in
the results they provided per se [e.g. 24, 25]. Since then, however, we have sensed little increment in such empirical studies — even though applications of method use have grown impressively. We continue to believe that it is especially important that decisions about whether to use Delphi (against using an alternative approach), decisions about which variant to use, and decisions about how to precisely enact one's chosen variant, be informed by sound (social) science. In enacting this agenda, it is important to be aware of research conducted in related literatures (as summarised here by Bolger and Wright [3]), as well as to appreciate important concepts such as validity and reliability and what these mean (or should, or can, mean) in contexts in which Delphi might be employed [17, 18]. Therefore our final urging is for researchers to take up this challenge of evidence, and ensure that scientific evaluations of the foundations of the method – established half-a-century ago – are strengthened and deepened