Table 1 shows the distribution over time of conceptual, empirical, and microeconomics model-based research papers in our database. Specifically, 177 of the 362 distinct papers in our database are primarily empirical, 130 are microeconomics model-based, and 55 are conceptual. The number of papers taking a purely ‘conceptual’ approach to channels research has evidently declined over time, while the numbers of empirical and microeconomics model-based papers have steadily increased, with microeconomics-based analytical models becoming more prominent of late.