The institute estimated 9,800 heat-related deaths between the beginning of April and July 19. The Robert Koch Institute attributed at least 5,100 deaths during that period to the heat. Heat, therefore, often does not appear on death certificates and is sometimes described as a "silent cause of death." The institute estimates heat-related mortality by comparing actual deaths during hot periods with the number normally expected at that time of year. Its monitoring is published with a delay because it relies partly on mortality figures compiled by the Federal Statistical Office.