Recent news reports suggest the average American wedding costs $27,000. But, there may be some important methodological issues with this figure: selection bias and using an average rather than a median.
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. Similarly, Brides magazine’s “American Wedding Study” draws solely from that glossy Condé Nast publication’s subscribers and website visitors. So before they do a single calculation, the big wedding studies have excluded the poorest and the most low-key couples from their samples. This isn’t intentional, but it skews the results nonetheless.
But an even bigger problem with the average wedding cost is right there in the phrase itself: the word “average.” You calculate an average, also known as a mean, by adding up all the figures in your sample and dividing by the number of respondents. So if you have 99 couples who spend $10,000 apiece, and just one ultra-wealthy couple splashes $1 million on a lavish Big Sur affair, your average wedding cost is almost $20,000—even though virtually everyone spent far less than that. What you want, if you’re trying to get an idea of what the typical couple spends, is not the average but the median. That’s the amount spent by the couple that’s right smack in the middle of all couples in terms of its spending. In the example above, the median is $10,000—a much better yardstick for any normal couple trying to figure out what they might need to spend.
Apologies to those for whom this is basic knowledge, but the distinction apparently eludes not only the media but some of the people responsible for the surveys. I asked Rebecca Dolgin, editor in chief of TheKnot.com, via email why the Real Weddings Study publishes the average cost but never the median. She began by making a valid point, which is that the study is not intended to give couples a barometer for how much they should spend but rather to give the industry a sense of how much couples are spending. More on that in a moment. But then she added, “If the average cost in a given area is, let’s say, $35,000, that’s just it—an average. Half of couples spend less than the average and half spend more.” No, no, no. Half of couples spend less than the median and half spend more.
When I pressed TheKnot.com on why they don’t just publish both figures, they told me they didn’t want to confuse people. To their credit, they did disclose the figure to me when I asked, but this number gets very little attention. Are you ready? In 2012, when the average wedding cost was $27,427, the median was $18,086. In 2011, when the average was $27,021, the median was $16,886. In Manhattan, where the widely reported average is $76,687, the median is $55,104. And in Alaska, where the average is $15,504, the median is a mere $8,440. In all cases, the proportion of couples who spent the “average” or more was actually a minority. And remember, we’re still talking only about the subset of couples who sign up for wedding websites and respond to their online surveys. The actual median is probably even lower.
These are common issues with figures reported in the media. Indeed, these are two questions the average reader should ask when seeing a statistic like the average cost of the wedding:
1. How was the data collected? If this journalist is correct about these wedding cost studies, then this data is likely very skewed. What we would want to see is a more representative sample of weddings rather than having subscribers or readers volunteer how much their wedding cost.
2. What statistic is reported? Confusing the mean and median is a big program and pops up with issues as varied as the average vs. median college debt, the average vs. median credit card debt, and the average vs. median square footage of new homes. This journalist is correct to point out that the media should know better and shouldn’t get the two confused. However, reporting a higher average with skewed data tends to make the number more sensationalistic. It also wouldn’t hurt to have more media consumers know the difference and adjust accordingly.
It sounds like the median wedding cost would likely be significantly lower than the $27,000 bandied about in the media if some basic methodological questions were asked.
Legally Sociable 