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Introduction
In many locations worldwide, daily time-series analyses have identified adverse associations between daily mortality and temperatures that are toward the hot and cold ends of the temperature range for each location (Gasparrini et al. 2015; Guo et al. 2014). Many of these analyses employed distributed lag models (Armstrong 2006; Schwartz 2000) that discount mortality displacement or harvesting (Zanobetti et al. 2000) within the lag interval, typically 2–3 wk in recent studies. However, they cannot identify the extent of displacement of mortality beyond this period. Such displacement may be quite short, for example, just a few months. The uncertainty about this makes it hard to estimate the actual life lost to weather and thereby judge the priority that should be given to public health policies to reduce those excesses.
One way to clarify the extent of mortality displacement due to the acute effects of heat and cold is to estimate associations between annual mortality and annual summaries of heat and cold. If such associations were null, it would indicate that excess deaths due to acute effects were wholly compensated by deficits later in the same year, as would be the case if all reflected mortality displacement. Positive associations of annual series would indicate that all or some of the excess deaths were displaced at least into the next period, suggesting that mortality was advanced by at least 1 y.
Two published single-city studies have used this method. In both London between 1947 and 2006 (Rehill et al. 2015) and Hong Kong from 1976 to 2012 (Goggins et al. 2015), years with cold winters and those with hot summers were associated with high mortality, though in temperate London, the association with heat was not significant. Those studies were not linked to daily studies, so it was not possible to directly estimate from them whether a proportion of heat and cold deaths found in daily studies were nevertheless displaced by less than 1 y.
In this multicountry study, we estimated the association between annual mortality and annual summaries of heat and cold in 278 locations from 12 countries. We also develop the method further to give insight, for positive associations, into whether the magnitude of association indicates partial or total absence of short-term displacement. This is easily...