How much does a wedding cost?
From The Wireless, because that’s where I happened to notice it, not because they did anything wrong
But the average wedding costs about $30,000 – equivalent to a down payment on a house, another comparable goal for a couple in their twenties.
That is the stylised number: you can find it in Stuff and the Herald and lots of other places. But what does it mean? Could it really be true that a typical couple spends about half their annual income on a marriage?
A One News story last year said
Nicky Luis, owner of Lavish Events in Auckland, said while there were no official statistics on the average cost in New Zealand, perceptions within the industry put the figure at $30,000.
That is, people working in the lavish-weddings industry perceive there to be lots of lavish weddings and think it’s normal to spend a lot of money getting married.
Even when the number is supposedly based on surveys there are problems, as Will Oremus wrote last year at Slate
The first problem with the figure is what statisticians call selection bias. One of the most extensive surveys, and perhaps the most widely cited, is the “Real Weddings Study” conducted each year by TheKnot.com and WeddingChannel.com. (It’s the sole source for the Reuters and CNN Money stories, among others.) They survey some 20,000 brides per annum, an impressive figure. But all of them are drawn from the sites’ own online membership, surely a more gung-ho group than the brides who don’t sign up for wedding websites, let alone those who lack regular Internet access.
To make matters worse, the summary quoted from the surveys is the mean, but the way the figure is used, a median would be more appropriate. Oremus extracts the information that the median is about 2/3 of the mean in those surveys, so we’re getting a 50% increase on top of the selection bias.
When you’re thinking about weddings you’ve been to, there is a different sort of bias. Expensive weddings tend to have more guests, so the average wedding you get invited to is larger than the average wedding you might have got invited to but didn’t.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »