Introduction

What has been the impact of COVID-19 on mortality? In this article I calculate, chart and explore excess mortality in the Netherlands during 2020. I find a very significant increase in the number of deaths during the year, above and beyond the ones expected to occur in the absence of special circumstances. The expected numbers of deaths come from statistical models with very good predictive performance. Most of the excess mortality can be directly or indirectly attributed to COVID-19, with a small exception related to a heat wave in the summer. The officially registered COVID-19 deaths account for three-quarters of the observed excess mortality. Excess mortality is considerably higher for men than for women. It is biggest for the 80+ age group, but it is also present for the age group 65-to-80 and even in the youngest age group 0-to-65.

The focus of this article is on the presentation and exploration of the excess mortality data. If you are interested in the methodology for estimating excess mortality and the details of statistical models, check out this step-by-step guide. If you are interested in how the data is assembled, see the files in the data preparation folder of this project on Github.

Excess mortality in 2020

To visualize excess mortality in 2020, first we load the pre-processed dataset that pools together data from CBS, ECDC and weather stations. We then estimate a robust linear regression model on the data from 2010 till 2019, and then we extrapolate from this model for 2020 to calculate the expected mortality for each week of the year.

The expected number of deaths is 153,577, while the number of deaths that were actually recorded during the year is 168,566, which is considerably higher - more precisely, it is 10% higher than the expected. Let’s see how mortality was distributed over the year. Based on the first few weeks before the first COVID-19 cases were registered in the Netherlands, it looks like our model is, if anything, over-predicting the number of deaths. Note that Week 1 and Week 53 are incomplete, which explains why they have lower numbers of expected and registered deaths.