Lies, damn lies, and self-reported sexual activity statistics

According to “Womens Hour” on BBC Radio 4, Tuesday 30 Aug 2016

“a US study” said that people born after 1980 (ie under 35) are having “less sex than previous generations”.  The study was published in the journal Archives of Sexual Behaviour (a journal I know from my Psychology degree).  I believe this was the August 2016 study “Twenge, J.M., Sherman, R.A. & Wells, B.E. Arch Sex Behav (2016)”, found at the URL below.

As the quote from the study below shows, the above BBC description of the study findings was a simplification.  The trend was more pronounced for women, but nonexistent for Black Americans, and for all college graduates.

“Americans born in the 1980s and 1990s … were more likely to report having no sexual partners as adults compared to [those] born in the 1960s and 1970s … The shift toward higher rates of sexual inactivity … was more pronounced among women and absent among Black Americans and those with a college education.”

I have removed the obscure US slang terms for the different generations.

The data came from the US “General Social Survey” (GSS), from people aged 20-24, who were asked about their number of sexual partners since age 18.  Thus the data and the finding relates to the age range of 18 to 24.

According to the same radio programme, the UK National Survey of Sexual Attitudes and Lifestyles “appears to show a similar pattern” in the UK.  However this too was inaccurate.  The “NATSAL 3” 2012 study does indeed show a continuing small decline in the median number sexual encounters over the past 4 weeks, but that was in a sample of the UK population aged 16 to 44, not 18 to 24 as in the US study.  The UK age range is thus very different from that of the US study above, which makes a direct comparison with the US figures impossible.

This self-reported UK decline in median sexual activity is relative to previous higher figures from 1999, and still higher figures from 1990.  The study was set up around 1990 because of the need for accurate statistics on the topic due to the AIDS epidemic, so those are the earliest comparable figures.

“On average over the past two decades there has been a decrease in how often people [aged 16–44] say they have sex.”

According to the BBC radio programme’s description of the 2012 NATSAL3 study, “1 in 5 people aged 16-24 said that they didn’t have a sexual partner.”

In fact the 2012 NATSAL 3 study reported that 19.8% of people aged 16-24 had *never* had a sexual partner, not that they currently lacked one.  The sloppy wording on the radio programme suggested more sexual activity had been self-reported than was actually the case.

To summarise:

o In the USA only *some* categories of people reported having less sex (when aged 18-24) than those born before 1980, not the entire US age cohort (as the BBC alleged).

o Contrary to the BBC report, the available UK data logically *cannot* tell us whether the same thing happened here (because the UK NATSAL age range studied is much wider than the US GSS one).

o UK data does tell us that a different age range from the US study (16-44) have been reporting less sex in 1999 than in 1990, and less again in 2012.

o The UK 2012 NATSAL data also tells us that 19.8% of people aged 16-24 reported *never* having a sexual partner, not (as the BBC claimed) that they “currently” lacked one.

I’ll leave the last word on the more interesting question (“Why?”) to the BBC.


Channel 4’s “Naked Attraction”: The Good, the Bad, and the Ugly.

Goodness that last political post was heavy and depressing, wasn’t it?  “… And now for something completely different”, a TV review.

This is the clipped, cleaned-up version, without any latin, or colloquial, terms for the human “naughty bits”.

Given that the series consists of attractive young men and women choosing potential partners based only (at first) on what they look like in the nude*, then what is my excuse for viewing this “filth”?  Well, this Channel 4 TV series is a cultural phenomenon (although I admit to not being as interested in “Bake-Off”).  I’m watching this new phenomenon closely so that you don’t have to!

(* When I say “nude” I really do mean completely naked, from all directions, and in close-up.)

The Good

The series was moderately inclusive, in terms of build, size, fatness, disability (including prosthetics), sexual orientation, occupations (an indicator of socioeconomic class), regional accents, and ethnic origins.  However I have seen nobody either old, nor ugly.  Potential advertisers and viewers would probably not have accepted that.

The Bad

The format was extremely shallow.  The “educational” content was minimal.  Things they could usefully have mentioned in particular contexts were left unsaid.  Having read “The Annals of Sexual Behaviour” for my Psychology degree tutorials, studied human evolution and development, I honestly think I could have provided more educational facts myself.

Throughout the series the term used to describe the external female “naughty bits” was actually the term for an internal organ.  That was a crime against language, and such incorrect terminology could promote confusion if used in a medical context.  (So much for “educational content”!)

The Ugly

It was essentially nude flirting, which could be regarded as pornography.  To my mind this should not be normalised by appearing on a mainstream TV channel, even after the 10 pm watershed.

The show exploits the exhibitionism of some young people, who should have been dissuaded for their own good.  It uses images of foolish people’s bodies to create marketable content (a sort of “naked Facebook” business model).

It’s dating for the Tinder generation, as the presenter is quoted as saying in The Guardian newspaper.  In my opinion, anyone who makes a decision about whom to date based primarily on physical attraction is probably heading for disaster.

Cancer incidence and “bad luck”

This one had even the presenters of the BBC’s weekly statistics fest “More or Less” scratching their heads.

The confusing abstract here: says

‘These results suggest that only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions. The majority is due to “bad luck,” that is, random mutations arising during DNA replication in normal, noncancerous stem cells.’

Tomasetti C, Vogelstein B. Variation in cancer risk among tissues can be explained by the number of stem cell divisions. Science. Published online January 2 2015.

Note the key phrase here “among tissues”, not “between individuals”. The study aimed to confirm the old and widely accepted theory that cancer is an inherent design flaw in all multicellullar organisms and that some level of cancer was an inevitable result of the rapid cell division that is essential for the maintenance of certain tissues (skin for example). However they did not look at cancer rates in individuals, only in different types of tissues.

Data was not available for all the possible tissue types. “Moreover, Dr Tomasetti and Dr Vogelstein were unable to include two of the most common cancers (breast and prostate) in their analysis, because the relevant stem-cell data are not available for these. What their study does explain is the long-known but curious phenomenon that apparently similar parts of the body suffer different rates of cancer. ”

This left the researchers with a relatively small set of data for tissues, from which it is hard to draw definite conclusions. “the estimate was quite variable, with 95% confidence intervals ranging from 39% to 81%. So only 4 out of 10 cancers may be a result of bad luck, or, alternatively, as many as 8 out of 10.”…/Are-most-cancers-down-to-bad-luck.aspx.

Also, according to coverage elsewhere (I’ve not seen the full paper), there were some exceptions to the general conclusion. “In some cancers [ie cancer types], environmental factors and inherited genetic factors did compound [ie significantly affect] the risk.”…/Are-most-cancers-down-to-bad-luck.aspx.

In particular, “The remaining third of cancer types, which are affected by [environmental] lifestyle factors, viruses or a heightened family [ie genetic] risk, include some of the most common:

Basal cell carcinoma – a type of skin cancer made more common by too much UV exposure
Lung cancer – strongly linked to smoking
Colon cancer – increased by poor diet and family risk genes”

One study alone is not enough to draw a definitive conclusion from. “Separate research by Cancer Research UK shows more than four in 10 of the total number of cancers were down to lifestyle.”

Also, even if the original study had been correctly interpreted and accurately reported, it would still be wise to avoid those risks that individuals can control, particularly smoking.

The original study was widely reported in the media as “the majority of cancer is due to bad luck”. However that was criticised in the Guardian. That article suggests that the only conclusion you can draw is that the majority of the variation in relative cancer risk between tissues is due to random genetic malfunctions during cell division. The key word here is “relative”, the implication is that the study says nothing about the actual absolute numeric risk of cancer in a particular tissue (not even in an individual person). The baseline risk across all tissues (if all cell division could be abolished) could take any absolute numeric value, from zero up to 100%.

The authors of the original paper seem to have retreated from their original headline-grabbing claim, now that their future careers have been boosted by the publicity. “We have not showed that two-thirds of cancer cases are about bad luck. Cancer is in general a combination of bad luck, bad environment and bad inherited genes.”
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