The expected number of deaths in the absence of a COVID-19 epidemic has been estimated based on the number of deaths in the preceding weeks, adjusted for seasonal factors. For weeks 11 to 20 it is assumed that the expected number of deaths per week is the same as in weeks 3 to 10. The first weeks of 2020 are not included in the assumptions because in weeks 1 and 2 there was a short flu epidemic that may have affected the number of deaths. In the weeks that followed, the number of flu-related deaths was estimated to be modest. The seasonal factors are adjusted for the average weekly temperature. It is assumed that every degree Celsius that this temperature is higher than the average temperature in weeks 3 to 10 leads to 1 percent less mortality. For weeks 11 to 14, the correction was very small due to little difference in temperature from weeks 3 to 10. From week 15 onwards it was warmer and the corrections were several percentage points.
Excess mortality is the difference between the observed number of deaths and the number that could be expected had no COVID-19 epidemic occurred, estimated by the method explained above.
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