Since some of this isn't completely obvious, and so I want to write this down for my own use later if nothing else, here's a post on
the difficulties of collecting statistics on the prevalence of rape. A
lot of this applies, in other forms, to collecting statistics on just
about anything that happens to humans, but because it's working
against privileged structures, statistics about rape get criticised
more for the same inevitable problems.
A lot of the problems aren't as important as they're made out to
be, though, from the point of view of having useful
statistics. (Furthermore, despite the problems, the statistics are all
relatively consistent to within an order of magnitude)
I'm discussing the problems here from the perspective of statistics
on victims; statistics on perpetrators have basically the same
sort of problems.
Definitions
The first difficulty is that the colloquial and
legal definitions of rape vary considerably. Colloquially rape is sex
without consent. Legally, this could be any of "rape", "assault by
penetration", "sexual assault" or "legal". Furthermore, the same
sexual activity could be rape if A does not consent, but "only" sexual
assault if A consents and B does not, because of the asymmetry in the
law discussing penetration.
This is to an extent an inevitable problem with the law. The Sexual
Offences Act 2003 defines "rape" and "assault by penetration" very
precisely. Everything else, whether it would generally be considered
rape or not, is "sexual assault". This matters, because the maximum
sentence for sexual assault is ten years, whereas rape and assault by
penetration have life sentences. Providing a loophole-free legal
definition of rape is the same problem as providing a loophole-free
definition of sex and adding "without consent" to the end of it.
Add to this the "reasonable belief" exemption in law that means
many things that the victim will call rape the law will call "legal"
or "no crime".
The problem comes, then, when you try to do any sort of measures of
prevalence. People will correctly say that they were raped when it
wasn't rape in legal terms. There seems to be some attempt to deal
with this in the British Crime Survey's figures on sexual assault,
which split "serious sexual assaults" (which include rape and assault
by penetration) away from "less serious" (indecent exposure, sexual
touching, sexual threats, etc: note that "sexual touching" is in law
the same crime as raping someone by forcing them to penetrate you)
If you classify according to the strict legal definition, then you
inevitably lose quite a few rapes in there buried in the sexual
assault and no crime categories. If you classify according to the
colloquial definition, then it becomes much harder to do comparisions
with the statistics produced by the criminal justice system (and
apologists will claim that your statistics are worthless because they
don't only include government-approved rapes)
There's also a question of whether to include the "attempted" types
of crimes within the statistics. I think that one should, because the
difference between the two is largely down to random circumstances,
and either way there's a rapist to apprehend: that they didn't get
quite as far as raping this victim (but far enough to make it clear
that they were going to try) shouldn't be considered.
Reporting
The second problem is that being a victim of rape has an extremely
strong stigma associated with it, and even if it didn't, as a
traumatic act it's something that some victims block out of their
minds. (Associated with this, misconceptions about consent aren't just
confined to rapists, so it's common for people not to define what was
done to them as rape until much later, even though they're dealing
with the psychological consequences immediately)
So it becomes very difficult to find out if people have been raped
by surveying them. The British Crime Survey tries to do this by asking
questions about actions rather than about legal definitions, and this
does help - around twice as many people will say that someone did
[action(s) constituting rape] to them than will say that someone raped
them. However, you then inevitably have the situation that the survey
is only as good as the questions are exhaustive (and even then despite
good methodology people may decline to answer).
We can use the surveys to establish some upper and lower bounds, at
least. The 2009/10 BCS data gives 0.4% of women and 0.1% of men, in
the preceding year, have been subject to rape, assault by penetration,
"serious sexual assault" and/or an attempt at either. We can't
necessarily scale up from this to a lifetime prevalence (if we for
simplicity assume the likelihood of being raped doesn't change with
age1 it gives a likelihood of 17.6% of women and 4.4% of
men, not all of whom will be raped in the legal sense).
The NSPCC
survey (page 66 onwards) gives figures for sexual violence of
around 27% for girls, 16% reporting that they were pressured into
intercourse (6% with physical force). There's no particular attempt to
match these up to legal categories, but it's obvious here that the
risk to 13-16 year old girls (not varying much by age within that) is
considerably higher than the average risk for the 16-59 year old
adults covered by the BCS. The NSPCC survey notes that figures between
4% and 78% have been found by other surveys of children, with - as
with adults - there being a significant gender split in perpetrators
and victims.
Meanwhile the Havens survey says that 41% of 18-25 year old
Londoners have felt pressured into unwanted sex. 9% of women in the
sample had said no and been ignored, and 25% of women (almost
certainly a strongly overlapping set) had said nothing and been
ignored2.
Measuring the legal system
It's relatively easy, within the provisos of the definition
problems, to get statistics on the legal process - convictions,
prosecutions, arrests, reports. Relying solely on those statistics is
a mistake: the attrition rate from report to conviction has worsened
considerably since the 1970s, while the number of convictions has
increased. What's happening is that rapes that wouldn't previously
have been reported - and marital rapes that were legal until 1991, for
that matter - are now being reported ... and the justice system hasn't
caught up.
There isn't any comparable prevalence survey going back that far -
the BCS only started asking about sexual violence in 2004 - but
despite everything, and despite appearances, the justice system is
probably better now (with its 90%+ attrition rate, and widely reported
failings) than it was in the 1970s with a much lower attrition rate -
because most of the attrition was occuring before reporting.
Measures from the justice system aren't useful for measuring
incidence of rape, but they are useful for measuring the
(in)effectiveness of the justice system (and hopefully improving
it). It's important, however, to note that the definitions problem
makes it very difficult to compare prevalence statistics with justice
system statistics (which makes getting meaningful figures about
reporting rates - beyond "very low" - very difficult indeed).
Another problem is that the categorisations used for reporting and
police activity - the report to charge stage - use one set of
categories (managed by the Home Office), but the categories at the
charge to conviction stages use a different set (managed by the
Ministry of Justice). This makes sense, because the police often won't
know exactly what crime has occurred until after they've investigated,
whereas the CPS and courts do know the details of the charges, but it
makes comparisions tricky. Kelly,
Lovett and Regan's attrition study dealt with this by following
cases right through the report to conviction process (or as far
through the process as they got, anyway).
The need for statistics
On the one hand, it doesn't really matter at this stage. It's very
clear from the statistics that the (lifetime) chances of being raped
(in the colloquial sense) are somewhere between 1 in 20 and 1 in 2 for
women (and most probably around the 1 in 4 figure generally quoted),
and lower (but still probably higher than most people would guess) for
men. Wherever it falls within that range, it's still a massive problem
(we view murder as a serious problem at the far lower 1 in
10003 lifetime prevalence, and rape is sentenced similarly)
On the other hand, if it's not to remain a problem, there's a need
for accurate statistics to monitor things over time, so that it's
possible to tell if actions to deal with the problem (by bringing
rapists to justice and more importantly because we
don't have space for all of them by educating people so they don't
become rapists).
Fortunately, for the purposes of accuracy, it doesn't matter than
much exactly what definitions you use, as long as you're consistent
over time. You'll always only be asking about - and being told about -
a particular subset of sexual violence, but you should be able to
measure trends in it. The way that rape culture works, it's
vanishingly unlikely that one particular form of sexual violence that
you're surveying will disappear or expand while the rest remain
unchanged.
As long as you remember that changes in methodology are likely to
give changes in result significantly larger than any change in the
underlying facts, then changes can be seen (and yes, this means
sticking with methodology you know is flawed, at least until you've
run it in parallel with the improvements for a few survey cycles to
see what difference it makes).
A final thing to note - and bear with me here - is that accuracy
can be overrated. For year-to-year comparisions about the scale of the
problem, a repeatable survey that's not too vulnerable to random noise
is needed. For surveys to establish the existence of a problem within
a particular context, it's not. There was a recent NUS Women's
Campaign survey looking at female university students' experience of
sexual violence, which gave the predictable results. It wasn't at all
statistically sound: self-selected sample, no attempt to normalise it
demographically, massive difference in response rates between
universities, etc. but that doesn't actually matter for establishing
the existence of the problem.
Now, if universities were to take the NUS survey seriously and
start doing (actually useful4) things to reduce sexual
violence on campus, then a survey less sensitive to random noise would
be needed. But if they were going to take it seriously they'd fund
their own surveys for that purpose, and if they're not going to take
it seriously a "yes, this is still a problem, what did you expect?"
survey is all that's needed.
Footnotes
1 I believe it decreases with age, but I don't have the
figures for that.
2 This brings us back to definitions. Silence is not consent, but the law usually takes it as such. But you'd never find out about this set of colloquial rapes/sexual assaults if you didn't ask that specific question.
3 Massive variation with gender, cis/trans status, age, race, class, sexuality, disability, location, etc. As a society we don't view the elevated number of murders of certain non-default individuals as a problem, even if the murder rate as a whole is considered a problem.
4 Putting up "have you considered not getting raped?" posters, for instance, is fairly common and massively counter-productive.