Hellin's law

Hellin's law is an empirical rule estimating multiple-birth frequencies: twins occur about once in 89 births, triplets once in 89², and higher multiples at successive powers.

Connect

Multiple birth: A birth in which two or more offspring are delivered from one pregnancy. Hellin's law estimates how often multiple births occur at each order.
Friedrich Hellin: A German physician and statistician associated with a nineteenth-century rule for multiple-birth frequencies. His name became attached to the powers-of-89 estimate.
Multiple-birth rate: The proportion of births in which two or more infants are delivered. This is the quantity Hellin's law is meant to estimate.
Poisson distribution: A probability distribution modeling counts of independent events occurring at a constant average rate. It offers a formal count model, unlike Hellin's simple empirical powers-of-89 pattern.
Multiple-birth epidemiology: The study of the frequency, causes, and outcomes of multiple births in populations. Population studies test how far observed rates still match Hellin's pattern.
Twin: One of two offspring produced in the same pregnancy. The law takes twin births as its baseline, about one per 89 births.
Historical demography: The study of past populations using records of births, deaths, and other demographic events. Historical birth registers supplied the observations behind early multiple-birth estimates.
Epidemiology: The study of how health events are distributed and shaped within populations. Testing the rule requires comparing multiple-birth rates across populations and periods.
Binomial distribution: A probability distribution for the number of successes in a fixed number of independent trials. It models counts from explicit trial assumptions rather than the law's observed ratios.
Fertility treatment: Medical interventions intended to increase the chance of conception or pregnancy. Changing treatment practices alter multiple-birth rates and weaken historical predictions.