*2.5. Linear Regressions*

To test whether different sets of data correlate directionally with each other over the long-run and in different climatic settings, we statistically compared the long-term trends between: (1) climate change and plague outbreak; (2) economic change and plague outbreak; (3) climate change and economic change; and (4) internal dynamics of economic change. For each set of correlation tested, we divided the study timespan into different climatic periods, namely: (1) warm periods (positive temperature anomaly); (2) cold periods (negative temperature anomaly); (3) dry periods (below-average precipitation with reference to AD1347–1760); and (4) wet periods (above-average precipitation with reference to AD1347–1760). To assess the afore-mentioned long-term relationship, we adopted simple linear regression models for each combination.
