Analysis of the Mortality Trends Using the Lee-Carter Model in Japan During Pandemic

The purpose of this study is to demonstrate the effectiveness of residual analysis using the Lee-Carter model in analysing age-specific mortality rates in Japan during the pandemic. As of the end of February 2023, the number of deaths worldwide due to the COVID-19 infection is estimated to be 3.8 million. Generally, deaths directly caused by COVID-19 were predominantly observed among the elderly. However, in Japan, although the number of deaths due to infection was relatively low, an increase in suicides due to depression and a decrease in accidental deaths during home confinement were also observed. When analysing the impact of COVID-19 on mortality rates, it is necessary to consider not only the direct effects but also secondary effects such as suicides. Life insurance companies often remove outliers in the calculation of premium rates and in the assessment of soundness. However, the results of this study suggest that, in analysing excess deaths from the baseline, it is necessary to consider not only deaths directly caused by COVID-19 but also secondary factors such as an increase in suicides and a decrease in traffic accidents due to COVID-19.　This study demonstrates that analysing the residual term of the Lee-Carter Model is highly effective as an example of a tool for analysing these secondary effects.