Monday, July 18, 2016

'Marriages that end in divorce' is not the same as the divorce to marriage ratio

Jim Rose has highlighted the following depiction of "the percent of marriages that end in divorce". The range of percentages from 9%  to 71% is fascinating. Naturally the question arises, where would NZ fit in? What colour would this country be?

The answer is....we don't really know.

According to Statistics NZ:

One half of all marriages ends in divorce

This frequently uttered factoid looks like a good reason to save money on an expensive wedding. But can it be true?

Statistics New Zealand’s Population Statistics unit records the number of marriages registered each year and tracks how many of these end in divorce. Analysis of this data shows that roughly one-third of couples who married in 1970 had divorced by their jade wedding anniversary (35 years). This suggests that two-thirds of marriages end in the death of one partner.

But aren't divorce rates increasing? Of those who married in 1980, one-third of couples had already divorced by their silver wedding anniversary (25 years). This is still well below one-half of all marriages.

The longest marriage certified by the Guinness Book of Records is 86 years, although there are longer marriages pending verification.

This myth is busted.

How did this myth arise?
There are roughly 10,000 divorces and 20,000 marriages in NZ each year. 10,000/20,000 = 1/2 – so one-half of all marriages end in divorce, right? Wrong! The couples divorcing in a year are not the same couples who marry in that year, but a subset of all those who married in preceding years and have not yet divorced (a much greater number than 20,000).

When measuring the frequency of an event in a population (eg divorces) it is important to express the number of events in the context of the population who are likely to experience that event (sometimes called the 'at risk' population). For divorces, that population is the estimated number of existing marriages (from all years past and present). The method used to bust this myth, where divorces are analysed by year of marriage, is known as a ‘cohort analysis’.

What the chart above actually shows is the divorce to marriage ratio. Based on that NZ would be 43% in 2015, or the same colour as the UK.


Brendan McNeill said...

Thanks Lindsay,

Even a rate of 43% of marriages ending in divorce is still too high.

I note that Ireland with its residual Catholic population has a rate of just 13%, albeit Spain that is also nominally Catholic has a divorce rate of 61%. Maybe they have a different theology in Spain, or more likely differing cultural expectations.

Anonymous said...

Expect Ireland's divorce rate to rise quickly because the Catholic church's influence has collapsed in the light of numerous scandals.

The Republic will follow Spain within a generation.