Temporality issues (sequencing, trajectories, critical junctures, volatility of policy mixes)
In addition to these spatial issues, the temporal aspect is obviously a constitutive dimension of policy instrument research. We know that time makes a difference in how instrument choices and patterns evolve and that temporal sequences is a crucial (Taeihagh et al. 2013; Justen et al. 2013a, 2013b) component of policy mix design and evolution. Through a specific organization of events over time, for example, policy instruments can undergo permanent effects and thus becoming highly institutionalized and/or generate positive/negative feedbacks. And policy solutions - a set of adopted policy instruments - at a given point in time may enshrine problems as well as specific tools that actors must eventually confront in the next decision-making moment.
Thus, negative and positive feedbacks of the adopted policy instrument(s) will inform the policy debate such that the adopted instruments will either be adopted or will result in a crisis at the critical juncture which could be then an occasion for a shift from the adopted set of policy instruments. Policymakers, for example, can proceed by layering, conversion and drift (Thelen 2004).
All of these terms, however, are not clearly defined or consistently employed by various authors working in the field and, in some studies, are used without an appropriate understanding of the underlying concepts or methods necessary to analyse and evaluate a policy mix.
Layering is thought to be the most commonly adopted process but layering can be done in different ways. That is, policy instruments can be assembled through processes such as packaging, patching, stretching, and bricolage (Howlett and Rayner 2013; Capano 2018) which range in terms of coverage and deliberativeness. At the same time, related to the produced effects, layering can lead to policy instruments mixed in a consistent, counterproductive and tense way (Capano 2019) or not.
However, if we know something about these general modes and types of policy instrument design, we are missing reliable empirical knowledge about the micro-components of these different kinds of processes. There is a need to consider the effect of policy formulation processes on the character and effectiveness of complex policy mixes (Feindt and Flynn, 2009; Kay, 2007; Larsen, Taylor-Gooby, and Kananen, 2006), for example when existing mixes developed unsystematically through processes of policy layering (Thelen, 2004; Van der Heijden, 2011; Carter, 2012; Howlett and Rayner, 2007; OECD, 1996). From this point of view then, we require better empirical evidence of the foundations of design/non-design continuum. This would mean, for example, better operationalizing concepts such as package and patching, as well tense layering, in terms of instrument-based content.
There are thus many empirical gaps when the temporal dimension is considered. For example, we know very little about whether and how the speed of the sequence can make a difference in terms of choosing one instrument or another and in terms of change or persistence of the adopted of policy instruments. Furthermore, another under-investigated dimension of the temporal dimension is the composition of the sequence itself: what are the events of the sequence? What can be the relations of the actors in the different events of the sequence itself?