Hazard of mortality at ages 30–74 by preceding and subsequent birth intervals, Swedish men and women born in 1938–1960. The analysis population for examining preceding birth intervals consists of individuals in sibling groups with at least three children, excluding the firstborn. The analysis population for examining subsequent birth intervals consists of individuals in sibling groups with at least three children, excluding the last-born. The reference category is a birth interval of 25–30 months. Error bars are 95 % confidence intervals