January 26, 2012

Unfaithful to the data, too.

When I were young, the Serious News Outlets  probably wouldn’t have admitted the existence of extra-marital affairs by non-celebrities, let alone written an article that’s basically advertising from an infidelity website press release.

In some ways the data are better-quality than most advertorials, because the website has complete data on its NZ members.  They have even gone as far as using population sizes for NZ cities to estimate their, um, market penetration, which varied across the five main cities by as much as 0.06%.  No, that doesn’t exceed the margin of error.

The Herald’s article starts off

If your partner supports National, has a PC, drinks Coke, eats meat, has a tattoo, smokes and is a Christian, be warned – they could be a cheater.

Leaving aside the gaping logical chasm in identifying website members as representative of all ‘cheaters’, what the data actually say is that more members support National, not that more National supporters are members.   As you may recall, we determined not so long ago that more New Zealanders of all descriptions support National than any other party, so that’s what you would expect for members of the website.   The proportion of National supporters in the election was 47%, among website members it’s 33%, so National supporters are substantially less likely to be members of the website than supporters of other parties. The proportion identifying as Christian among website members is very similar to the proportion in the 2006 census.   79% of website users are on PC (vs Mac).  Again that’s a lower proportion of PCs than in the population of NZ computers (the Herald said 10% were Macs in July 2010, and for Aus+NZ combined, IDC now says 15%) but one explanation is that Macs have more of the home market than the business market.  More members drinking Coke vs Pepsi is also not surprising — I couldn’t find population figures, but Coke dominates the NZ cola market.

The story doesn’t say, but we can also be pretty confident that the website members are more likely to be Pakeha than Maori, more likely to be accountants than statisticians, and more likely to have a pet cat than a pet camel.



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 »


  • avatar

    I think you will find people in the cheaters category are also more likely to have a pulse and breathe… the stats on people cheating on their spouses who do not posses these things are incredibly low. the moral of the story? don’t trust your spouse as long as they are breathing? believe any twist writers put on the stats to make them appear to be saying something they are not? or stop reading the herald, and pickup a fiction novel instead. there’s probably more fact in in anyway :D

    5 years ago Reply

  • avatar

    Is it even plausible that there are 54,000 Ashley Madison members in New Zealand? It’s a website for married folks looking for affairs. There are what, 4.4 million people in the country? So more than 1% of the TOTAL population, never mind the adult married population, are purported to be members of the site?

    You nailed it when you called it an advertorial. Dating websites are network goods; if folks think there are more members, more will sign up.

    5 years ago Reply

    • avatar
      Thomas Lumley

      I was surprised by the 54,000 claim as well, but in the end I decided that for all I know it could be true.

      It’s presumably the number of accounts, and we don’t know how many duplicates there are. Also, there are probably a lot of people who signed up to look around the site, rather than with any real intent of using it.

      There are claims on the internet that all dating services inflate their numbers, but I didn’t see anything specific and concrete about this one in a brief search.

      5 years ago Reply

    • avatar

      Eric, it doesn’t sound impossible. TradeMe boasts of having 111,075 people online while I’m typing this and 2.9 million active members. Clearly TradeMe will appeal to a broader section of the population than a site on cheating.

      I assume that to be cheating you have to have in a relationship (marriage or de facto). NZ has roughly 21,000 marriages and 9,000 divorces per year; when adding de facto relationships, there is plenty of membership material for the site.

      The ‘article’ still reads like a pre-packaged press release though.

      5 years ago Reply

  • avatar

    Great! If I am questioned by my wife I can reply “don’t worry, I use a mac and don’t drink Coke”. Perfect alibi.

    5 years ago Reply

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