Posted by Jim Lindgren:
The Sex and Money Study Is Misleading.--
Todd Zywicki [1]mentioned the release of a study of sex, money, and
happiness by economists David Blanchflower and Andrew Oswald. When I
followed the [2]SSRN link he gave, it required $25 to download it.
Instead, I went through my university's online library card catalog,
which directed me to a free link for university subscribers, so others
at universities might try to get the paper for free that way. The
Blanchflower/Oswald article was first posted online last May as a
working paper on SSRN and the [3]National Bureau of Economic Research
.
In June, the study caused a flurry of comments, from the Wall Street
Journal to the Jay Leno show. The main finding discussed in public was
not the one that Todd noted (that sex leads to happiness), but rather
that those with higher incomes did not have sex more often than those
with lower incomes. But it appears that actually people with higher
incomes do have more frequent sex, as I discovered when I reran some
of their analyses using the same database they used, the General
Social Survey.
Unfortunately, in their May working paper Blanchflower and Oswald had
misunderstood the database they were using and all their data analysis
needed to be redone (as they agreed when I pointed this out to them).
Let me explain. In their working paper, Blanchflower and Oswald were
under the impression that the General Social Survey (GSS), which they
used, was a random sample of individuals. But the GSS, like nearly all
large surveys of the general public, is a multi-stage probability
sample, not a random sample. More seriously, the GSS is a household
survey, not an individual survey. They interview only one person in
each household. If you don't weight their results by the number of
adults in the household, then households with only one adult are
oversampled compared to married couples or larger households. For
example, in their working paper Blanchflower and Oswald reported that
22% of subjects reported no sexual partners in the last year. Once one
properly weights for household size, the real numbers for people in
their database, the 1989-2002 GSS, is 17.6% having no sexual partners
in the last year. People who live alone have less frequent sex, so it
is important not to overweight those who live alone.
In the article they just published, Blanchflower and Oswald corrected
this error as well as a minor one that I also pointed out in an email
to them. They reran their data accounting for the number of adults in
each household, and acknowledged my help in recommending the weighting
protocol that they used to do this.
Last summer I raised one other concern that they did not substantially
deal with in the final paper. And as I rerun numbers tonight using the
same database they used, I think this third concern is even more of a
problem than I thought when I corresponded with them last summer. That
is the finding that was most trumpeted by the press in June, that
money does not buy sex. In their published paper, they write:
What is the connection between income and frequency of sex?
Interestingly, Table 5 finds that it is zero for both men and
women. We know from these equations that money does seem to buy
greater happiness. But it does not buy more sex. In both columns 5
and 6 of Table 5, family income enters with rather weak t
statistics.
But the simple correlation in the GSS database that they used between
family income and the frequency of sex is .12, which is statistically
significant. (Also significant are measures more commonly used for
ordinal variables, such as Somer's d, gamma, Spearman's rho, and
Kendall's tau.) So, contrary to their paper, there is a "connection
between income and frequency of sex." Why didn't they find any in
their Table 5? The answer is that Blanchflower and Oswald did
regression equations that computed the effect of family income, net of
other predictors, such as marital status and full-time employment.
The Blanchflower/Oswald study finds that married people have much more
frequent sex. And the GSS shows that married people have much higher
family incomes, in part because they often have two incomes to pool.
Thus, it is not surprising that the relationship between family income
and sexual frequency is primarily through the path of marital status.
So net of marriage and some other variables, family income has no
additional effect. Another way of saying this is:
1. Adults with higher family incomes have somewhat more frequent
sex. 2. This is mostly because married people have much more sex,
and adults who are married tend to have much higher family incomes.
Thus, people should recognize that there is a positive relationship
between income and sexual frequency, but this relationship occurs
through other variables (such as marriage) that are related both to
sexual frequency and to family income.
References
1. http://volokh.com/archives/archive_2005_01_00.shtml#1104871340
2. http://papers.ssrn.com/sol3/papers.cfm?abstract_id=623334
3.
file://localhost/var/www/powerblogs/volokh/posts/www.nber.org/papers/w10499
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