A Figure in Flight

Are nearly half of flights taken by men aged 20–45 for stag dos?

The environmental charity Hubbub claimed “half of all flights taken by men aged 20–45 were for stags”. Their environmental campaign aims to encourage less flying. This figure received widespread media coverage.

Based on survey estimates, Hubbub made an inadvertent calculation error. The Censuswide survey estimates are implausible, suggesting over 6 in 10 men went on a stag do in 2019.

Why wing it?

Hubbub claimed “half of all flights taken by men aged 20–45 were for stags”. The original report stated this figure came from Censuswide.

Why though?

News organisations reported this claim. Media coverage included the BBC, The Times, Daily Mirror, Metro and Euronews. On Twitter, Stanley Pignal (The Economist) and Anthony Wells (YouGov) examined the claim.

I also contacted the charity, querying this statistic. Hubbub were open and transparent about the commissioned survey. The exchange also showed how Hubbub calculated this figure.

Take the right altitude to flying statistics. (Image: Pixabay/bilaleldaou)

Censuswide conducted a survey of 2,002 UK adults aged 20–45 via an internet panel. Their survey received responses between 20th and 25th November 2019.

Hubbub had taken the mean average responses to two questions:

Q2. In 2019 how many hen, stag or sten dos involving an overnight stay have you been on/will you go on?

Q25. By the end of 2019, how many return flights will you have taken over the course of the year? Eg. Barcelona and back = 1

For men in Q2, the mean average number of stags do involving a flight abroad was 1.00. For men in Q25, the mean average number of return flights was 2.05. Dividing the former figure by the latter gets 49%, or about half.

There is a major issue with this calculation.

Respondents who answered they have “never been on a hen, stag or sten do” in the first question are not offered Q2. The mean number of stag dos is the average among men who report going on such a party.

We can adjust the calculation — setting those said they had never been a stag do to 0. After this change, the self-reported mean number of stag dos involving a flight abroad is about 0.8.

Following the calculations gives a proportion of around 40%. The same method for women gives 28%. This is the calculation that Hubbub intended to make. The charity have updated their press release. These statistics remain implausible.

The strange survey

There are 12 sub-questions in that second question. Each respondent must say how many hen dos, stag dos, and “other celebrations” they had been on. These three types splits into going in the UK or abroad, and travelling by plane or not.

Self-reported flights in that question outnumber return flights later in the same survey. This may be coherent for some respondents. They could be taking a round trip.

Self-reported behaviour may not match real behaviour, due to false recall and other reasons.

There are other strange artefacts.

Censuswide have not applied weights by gender. Men are 39% of their sample, rather than around half.

Respondents answered an open question about “ideal activities on an ideal trip”. This open question received nonsensical responses like: “good brand” and “great product”. Pew Research Center have suggested non sequitur answers may show bogus respondents.

In the Censuswide survey sample about stag and hen dos:

  • 62% of men and 54% of women went on such a trip in the UK in 2019;
  • A higher proportion of men went on a hen do than women.

We can see the implausibility of this survey statistic.

In England and Wales, the ONS reports there were 249,793 marriages in 2016. For Scotland in 2016, NRS records 29,229 marriages. NISRA states there were 8,306 marriages in Northern Ireland in that year. Across the UK, there were less than 290,000 marriages in 2016.

The ONS mid-year population estimate in 2018 for men aged 20 to 45 was 11.2m.

There are similar estimates of men and women aged 20 to 45. (Image: ONS)

Assume the following:

  • 290,000 men get married;
  • Every man has a stag do;
  • Non-overlapping groups of 15 men attend every stag do.

Those assumptions would make less than 40% of men attending a stag do. The Censuswide survey estimate is the average man aged 20–45 attended 3.3 stag dos in 2019. This estimate implies over 125 men went to the average stag do party.

A YouGov survey in August 2016 estimated 62% of men had ever been a stag do. This figure was for all GB men, aged 18 and over. By comparison, the Censuswide sample reported 83% had been a stag do, hen do or other celebration (“sten do”).

For whatever reason, most of Censuswide’s sample self-reports going on stag dos and hen dos last year.

An environmental charity commissioned a survey in good faith. The survey estimates underlying their statistic appear implausible.

Surveys provide estimates, subject to many sources of potential error. Sometimes, surveys can go very wrong.

This blog looks at the use of statistics in Britain and beyond. It is written by RSS Statistical Ambassador and Chartered Statistician @anthonybmasters.

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