Excess mortality rate is a measure of the increase in the number of deaths during a time period and/or in a certain group, as compared to the expected value or statistical trend during a reference period or in a normal situation. It is a more comprehensive measure of the total impact of a crisis, such as a pandemic, on deaths than the confirmed death count alone. Excess mortality can be calculated by subtracting the expected number of deaths from the observed number of deaths. It can also be expressed as a percentage of additional deaths compared with a baseline period. Excess mortality can be caused by various factors, such as heat waves, cold spells, epidemics and pandemics, famine, or war. It is also studied for certain groups of people, such as the elderly, men, and the unemployed. Excess mortality can be used to estimate the mortality caused by events combined with other indirect health effects.