We argue that behavioural public policies (BPP) should be categorized by the kind of mechanism through which they operate, not by the kind of treatment they implement. Reviewing the energy consumption BPP literature, we argue (i) that BPPs are currently categorized by treatment; (ii) that treatment-based categories are subject to mechanistic heterogeneity: there is substantial variation of mechanisms within each treatment type; and (iii) that they also display mechanistic overlap: there is substantial overlap between mechanisms across treatment types. Consequently, current categorizations of BPPs do not reveal the conditions of their efficacy and should be revised to better reflect mechanistic information.

Mixed-methods research (MMR)—the combination of qualitative and quantitative data within the same design to strengthen causal inference—is gaining prominence in the social sciences but its benefits are contested. There remains confusion over which methods to mix and what is the point of mixing them. We argue that variety of evidence is what matters, not of data or methods, and that distinct epistemic principles underlie its added value for causal inference. The centrality of evidential variety also implies that strong causal pluralism is untenable as a foundation for MMR.

In this paper, we analyse the difference between two types of behavioural policies – nudges and boosts. We distinguish them on the basis of the mechanisms through which they are expected to operate and identify the contextual conditions that are necessary for each policy to be successful. Our framework helps judging which type of policy is more likely to bring about the intended behavioural outcome in a given situation.

The article argues for the epistemic rationale of triangulation, namely, the use of multiple and independent sources of evidence. It claims that triangulation is to be understood as causal reasoning from data to phenomenon, and it rationalizes its epistemic value in terms of controlling for likely errors and biases of particular data-generating procedures. This perspective is employed to address objections against triangulation concerning the fallibility and scope of the inference, as well as problems of independence, incomparability, and discordance of evidence. The debate on the existence of social preferences is used as an illustrative case.