Ratio of difference between the number of live births and deaths to population in the middle of the period or to the average population during this period.

Natural increase rates (as well as rates for other vital statistics events) for different periods (month, quarter, half year, three quarters, etc.) are calculated on an annual basis, i.e. that the examined facts recorded in a given period increase accordingly to the annual volumes, e.g. for the rate calculated for the period: - month - the number of facts is multiplied by 12, -quarter - by 4, - half of the year - by 2, -three quarters - by 4/3.