When it comes to sex and censorship, Government's insistence that laws are "evidence-based" is little more than hot air.

The statistics quoted in support of any given case are frequently misleading, partial, and - according to one expert in this field - subject to highly unethical collusion of interest between government and researchers.

From rape to lap-dancing, from internet harm to obscure sexual practices, "evidence" is used to back a narrow politicised agenda, rather than as a basis from which to develop policy.

A good – or bad example – of this approach can be found in the Lilith Report on Lap-dancing, produced in 2003, which sought to link sex crime in Camden with the opening of local lap-dancing clubs.

Sponsored by Eaves Housing For Women – of whom more later - the report quoted, without full context, some selected figures: over a three-year period, the level of sexual offences in Camden fell by less than in two allegedly comparable boroughs, and the level of recorded rape and indecent assault in Camden increased by 50 and 57 per cent following the establishment of two mainstream lap-dancing establishments.

As "research" goes, this contains more holes than the proverbial Swiss cheese. We asked the Eaves Project for comment, but at time of writing had not received an answer.

It is an absurdly simplistic "correlation equals effect" argument, with virtually no controls of any kind. Yet such is the political desire that this report be true, it is quoted frequently and as gospel – from the Guardian to Amnesty’s official site - whenever a journalist wishes to take a pop at lap-dancing.

But then, it was ever thus. The first and ground-breaking research into sexual behaviour was the 1948 Kinsey report in the United States, followed by Mass Observation’s "Little Kinsey", whose findings – including a high level of homosexual experimentation and marital infidelity - were considered so shocking that they were, in typical UK fashion, kept secret for decades after.

Kinsey came in for serious academic criticism on the grounds of sample selection (volunteers who came forward for interview were mainly self-selected) and sample bias (a high proportion of prison inmates and prostitutes). This in turn led critics to argue that both Kinsey’s focus and findings were coloured by his own interest in masochistic and promiscuous sex.

However, a subsequent re-working of Kinsey’s data suggested that the sample bias had little effect and that in general, people’s sex lives were more colourful and more varied than conventional moralists liked to imagine.

Convenient categories

The problem with evidence-based policy in this immensely controversial area start here, with basic categorisation. They are then compounded by selectivity within the research, with government in particular keen to select measures, sample, reports, and effect to suit their basic agenda.

According to Kinsey, around one-third of US men had at least one homosexual experience in their lifetime. Does that mean that one-third of Americans are gay? Probably not.

What then is the meaning of "being gay"? A spat is currently developing between Consenting Adult Action Network (CAAN) and the Equality and Human Rights Commission (EHRC) over the nature of "sexual orientation". According to the Equality Act 2006 (pdf), the EHRC is concerned with inequalities which affect a variety of groups – including groups defined by their "sexual orientation."

Clair Lewis, National Convenor for CAAN, asked the EHRC why they view homosexuality as an orientation – but not, say, sado-masochism. For the EHRC, Director of Public Policy, Andrea Murray, argues that the EHRC is limited to what the law allows it to consider, and that by definition, “orientation” excludes bdsm: CAAN remain unconvinced and have indicated that they consider this to be ducking the question, that the only answer they have received to date is a hint from their Chair, Trevor Phillips that the difference lies in whether someone is "born that way” or makes a conscious choice.

Whilst such a view may apply to gender, it is questionable whether the nature/nurture argument can ever be so clear in respect of behaviour. In general, genetic causation is not a fixed effect, but varies according to the levels of social variability to which an individual is subject. In a highly regulated society, in which social effects have been minimised, the proportion of genetic causality behind any behaviour will increase - and vice-versa, in a society where difference is tolerated, the genetic effect will diminish.

This issue of categorisation shades into questions of measurement selection in the much more serious area of rape. It is a commonplace of news reporting that the number of rapes has gone up over the last few decades from 1,200 reported in 1980, to over 12,000 in 2004-5, whilst the conviction rate has dropped from a relatively re-assuring 38 per cent to a mere 5.5 per cent in the same period.

The problem with such Shock!-Horror! comparisons is that a complex picture is reduced to a few very basic measures. Conviction rates (here, the ratio between crimes reported and convictions obtained) has plummeted for almost all categories of crime in the same period - and to similar degree. The current conviction rate for rape is certainly not good – but it is not out of line with that for many other offences, such as wounding or burglary.

Public perceptions of what constitutes rape – and so the threshold for reporting an incident - have almost certainly shifted over the period, whilst the basis for even such basic measures as recorded crime has changed.

Poppycock problem

Is a trend remotely charitable? Possibly – but only by professionals, who are aware of the underlying factors that affect the figures. The debate is not helped by women’s groups who report far higher incidences of unreported "rape" based on self-identification by "victims" and compound this with assertions that only a very small proportion of victims lie about such matters.

The difficulty here is definitional: It is very likely that many if not most of the women making such claims are correctly asserting that they have suffered a traumatic experience. But, as a crime, whether rape takes place or not depends on the perception of the perpetrator - whether or not he had reasonable cause to believe that consent was present.

Whilst the conviction rate for cases that get to court is considerably higher than 5 per cent (hovering around 50 per cent), it is a long way short of the 97 per cent implied by the claim that women rarely lie about such matters. Are 50 per cent of victims therefore lying? Absolutely not.

Courts are, however, acknowledging a difference in perspective between alleged victim and perpetrator that is almost certainly not resolvable in any straightforward fashion.

This issue of self-reporting is also at the heart of numerous studies that purport to demonstrate attitudes on sexual issues.

One study asked respondents whether violence towards a partner "could ever be" justified – and then used the results from this loaded question to proclaim that a high proportion of young men believed it was ok to hit their girlfriend. The best measure of behaviour is not what people say, but what they do – their "revealed preference" as economists term it – and basing policy on how individuals respond to surveys is particularly dangerous.

A furious debate on the measure used is also at the heart of questions raised in respect of proposed legislation on Trafficking. Provisions introduced in the Police Bill 2009 would make it a criminal offence to purchase sex from any individual who had been trafficked.

The rationale for this law is "research" put together by the Poppy project and other anti-prostitution groups that claims that the number of trafficked women in the UK runs into the tens of thousands. One report put the figure as high as 80,000.

On being questioned with regard to the academic credentials of their research, Poppy rather huffily suggested that this was an attempt to silence them, and they had as much right to publish research as anyone else.

Against that, the numbers of trafficked women that the police have actually managed to find are vanishingly small. A six-month investigation involving over 800 brothels turned up just 167 possible victims

Extreme porn

Another issue that echoes criticism laid at the door of Kinsey, lies in sample selection. Supporters of the recent legislation on extreme porn were keen to talk about its effects on rapists. Other research has focused on interviews with convicted paedophiles.

Both police and pro-censorship academics, in their contribution to consultation on this law, talked about how individuals who had been convicted of sex crimes had owned up to using porn prior to commission of their crime. As arguments go, this is even less useful than the "slippery slope" argument about cannabis leading on to hard drugs.

It is looking at the issue backwards: By selecting for research a group who are already implicated in extreme activities, it is scarcely surprising to find that they use pornography. Worse, those interviewed have a vested interest in finding excuses for their behaviour and coming up with a picture that conforms to any bias they expect the researcher is looking for.

Which is easier? Taking responsibility for the awfulness of the crime that you have committed? Or claiming, in effect, that "the porn made me do it"?

In fact, research needs to look at the entire population and its porn-using habits – and then look for any causal link between level of use and offending outcomes.

A constant concern in any academic research is report selection: This is where researchers and policy-makers carefully handpick the papers and evidence that they will use to support their case. As already noted above, when it comes to sexual conduct, the Government seems very interested in the work of avowedly partisan bodies such as the Eaves project and the Poppy Trust.

This linkage was made explicit recently in a polemic by psychologist Belinda Brooks-Gordon, who highlighted the unhealthy relationship between these organisations and government. The latter need research to support its policy positions in the area of sex and sexuality. Organisations receive funding from government for research; the more positive results they come through with, the more likely it is that funding will continue.

Government are also fairly selective when it comes to putting out consultations in the first place. The usual suspects, when it comes to any matter regarding sex and sexuality will include most police forces, plus other police bodies, such as ACPO and the Police Federation, plus children’s, church, and women’s groups.

The insistence on seeking input from police forces, together with the fact that forces may sometimes liaise or talk to ACPO about their position on particular issues creates a fairly predictable block vote. The inclusion of children’s groups may tug a few heart strings – but is of questionable relevance on issues where the debate is about adult sexuality and what adults do with other adults.

The other side

When it comes to the "other side", the government consultation on extreme porn was very limited in seeking input from groups representing the bdsm community. Their invitation to Spanner, one of the oldest and most distinguished groups in this area was sent to the wrong address.

Proposals in respect of "cartoon porn," currently before parliament, appear to have been put together with little or no input from any official industry trade body – which may be why the government declared with such confidence that the proposals would have no discernible effect on UK commerce.

However, it is in the area of presumed effect that government law-making is most shaky. The basic Libertarian argument, derived from John Stuart Mill, is that government may make laws where issues of direct harm to individuals are involved.

Unfortunately, across a range of issues, from porn to video nasties, the received wisdom is that there is no such evidence. That does not mean no link exists: Rather that the research that might show such a link beyond any reasonable doubt has not yet been carried out.

When the government was legislating on the content of videos in 1984, a series of claims were made, many based on unsubstantiated media stories, about links between watching videos and subsequent behaviour. These claims were later comprehensively debunked by a number of academics, including Guy Cumberbatch of Aston University – and to their credit, the Department of Culture, Media, and Sport (DCMS) accept this.

What then is government to do? The answer has been twofold – and neither answer does them much credit.

On the one hand are attempts to redefine the concept of harm. One argument that has been developed by feminists is that there is such a thing as "harm speech" - that words can do harm in respect of how they frame a particular group socially and therefore create social consequences for that group.

Whilst this may inform some government thinking, it is not uppermost. More interesting is the concept of "potential harm" or "risk of harm." The former appears in the Video Recordings Act 1984 and has been given added weight in the last year by a ruling that the BBFC should pay attention to risk of harm when classifying films.

The DCMS argue that children shouldn't be exposed to certain kinds of content because it could be harmful. A Westminster Hall debate on "Harmful Content on the internet" produced some intriguing assertions about risk, as Conservative MP, John Whittingdale, observed: "If one looks for empirical, hard, factual evidence [of harm], there is very little. Our view was therefore not...'we cannot act,' but that we should act on the probability of risk."

It is hard to understand what the government and politicians are getting at here. Almost everything is potentially risky. We asked the BBFC why they were happy to censor films on the grounds that some sexual practices were "potentially risky" whilst leaving alone smoking, despite the known hazards that involves. Their answer is that public acceptability is also a factor. Or, in other words, potential risk is important ...sometimes.

Careful selection

The other way in which government manages to skew evidence for its policies is in the careful selection of the criteria it sets out to measure. Following on from an original assertion that there was no evidence for harm resulting from extreme porn, it put in place a Rapid Evidence Assessment which quickly concluded that after all, there might be some evidence.

This report has been widely criticised – not least on the grounds of the assumed bias of its authors. However, a far more serious criticism of this work is that it was scoped to report only on evidence for harm.

According to the Royal Society for Prevention of Accidents (pdf), Christmas trees, household linen, and underwear are all associated with some degree of harm. So should we ban underwear?

Any report on any subject that is directed to find harm is likely to do so to some degree. The real question is whether the topic under review causes net harm. Opponents of the extreme porn law have argued that the net effect of porn is to reduce overall sex crime in societies: The government review did not address this question. Nor did it report on instances where material reviewed showed positive harm reduction effects from porn.

It was essentially lopsided.

In closing our review of evidence in government policy-making, an honourable mention to Martin Salter MP, who has persistently talked up the evils of "Snuff" movies – despite numerous reports arguing that any such trade, if it exists at all, is tiny. A mention too to Keith Vaz, MP, who continued to claim that the killers of British schoolboy Stefan Pakeerah had been influenced by the video game Manhunt, despite police evidence that they had probably never seen it.

Congratulations also go to the BBFC, who are happy to quote the advice of experts when making their decisions – but who prefer not to name the experts concerned.

Pride of place, however, goes to the Home Office Committee charged with reviewing Sexual Offences back in 2000. In their report, "Setting the Boundaries" (pdf), they expressed surprise that necrophilia wasn’t actually a crime. They could find "no firm evidence of the nature or the extent of the problem," but, since they thought most people would expect it to be illegal anyway, had no problems with proposing its criminalisation.

That’s evidence-based policy-making for you! ®