The Other Swedish Model

Gender, sex and culture, by Laura Agustín
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Trying to prove Swedish law reduces trafficking: Garbage in, garbage out


I’ve been researching undocumented migration and trafficking for 15 years now. My book Sex at the Margins: Migration, Labour Markets and the Rescue Industry shows how the usual generalisation of undocumented migrants as victims is a patronising first-world construct. That’s not to say there is no injustice or sexism and it’s not to say all migrant women who sell sex are ‘happy’. Since the book was published in 2007 my blog Border Thinking has become well-known amongst people interested in an approach to migration, trafficking and the sex industry that questions many conventional ideas. Rather than engaging in repetitive ideological debates I critique research methods, media treatments, political and social-work rhetoric and any effort to squelch the voices of those involved, whether they call themselves migrants, prostitutes, entertainment workers or anything else.

Recently Swedish government evaluators said that the 1999 law against buying sex helps stop trafficking. They provided no credible evidence, which not only I but numerous other commentators noted (see earlier posts on this blog). Last week newcomers to prostitution and sex-industry issues claimed to have showed how a statistical model proves the Swedish law does reduce trafficking. They did it on a blog, with ‘The Law and Economics of International Sex Slavery’, a working paper – a term academics use when they haven’t published an article yet in an academic journal. Journals send contributors’ submissions out to be reviewed by people in the same field; the process, called peer review, is usually double-blind, which usually means neither writer nor reviewer know the other’s name. This is not always required with a university-published ‘working paper’.

The authors engaged briefly with me, Louise Persson and others on Niklas Dougherty’s blog, shortly after Louise and I published an article critiquing the government’s evaluation on Svenska Dagbladet. Niklas queried some of the information claimed by the authors, pointing out the egregious error they committed when accepting erroneous Danish figures on street prostitution – data that was debunked in the Danish parliament last year as well as in the media more recently. I find it inconceivably irresponsible that researchers desiring to present themselves as ’scientific’ would use known false data.

On Niklas’s blog (see comments), I confronted the authors for failing to recognise that the ‘data’ they claim to be using is inherently faulty and therefore unusable. I said

It’s a fantasy to think you can talk about ‘data’ when there is not agreement about who is to be counted. Some counting projects call all women migrants who sell sex trafficked. Others call all undocumented migrants trafficked. some call all women who sell sex trafficked. The numbers come from small ngos and police departments who use different definitions and often admit to being confused.

I also take exception to being given evidence from tiny, super-homogeneous places like Bergen (Norway). Nordic research is about very small places with recent, short histories of in-migration, undocumented migration being even smaller. It is misleading and silly to compare ‘data’ from such sites with whole large countries with long and varied migration histories.

The defensive (and inexperienced) response was to accuse me of being anti-science. This is nonsense. The principle here is known everywhere as Garbage In, Garbage Out: it doesn’t matter how pretty your statistical model looks or what a fancy machine you have to crunch the numbers in if the original information you put in is rubbish, and I am far from the only one to think so. The ’science’ we want to see is honest.

Here is the peer review the authors would have received had their working paper been sent to Paula Thomas, mathematician and statistics analyst in the UK (and if you are cowed by the language, look at the final paragraph).

Comments on The Law and Economics of International Sex Slavery

1. The vector X_i

Only indicative information is given as to what this is. We are told (p12) that it includes population, GDP, migration share (is this immigration only?), heroin seizures and a measure of the rule of law. It would appear that there were other things in the vector but we are not told what they are.

But the main weaknesses here are threefold:-

(a) The use of categorical data

Categorical data is, in my view, dangerous, because:-

(I) It imposes value judgements.

(II) More seriously it obscures the extent of a problem whilst appearing to clarify it.

(II) Is best illustrated using crime figures. London’s Metropolitan Police Service has an excellent crime mapping system. However it does have some weaknesses, and the one that is relevant here is its use of categorical data (fortunately this is mitigated by the use of actual figures as well). My own area went from above average for residential burglary in May 2010 to low for June 2010 on the basis that there were 3 fewer crimes! Do I need to say more?

(b) The lack of any attempt to model (Delta Trafficking), that is the change in trafficking over time.

(c) The lack of any clarity regarding how the weighting variables beta_0 and beta_1 were chosen. In particular doubt must surround beta_1 as it is a single weighting for a whole vector and the elements of the vector have different units, so some dimensional analyses should have been performed.

It would be most helpful if there was a proper ‘methodology’ section explaining the processes used to get the results quoted.

2. The model used

The model is a Logistic regression model the normal formula for which is:-

z=beta_0+sum(from i=1 to n)(beta_{i} x_{i})

Normally this model only applies where the the data are modelled by a binomial distribution.

One question then must be is the data here binomially distributed? This is for the originators of the report to justify.

I also notice the use of a ‘normally distributed error term.’ What error is this term expressing? And how?

Another point is that the variable ‘z’ is not used directly. The probability calculation is:-

P(event=yes)=1/(1-e^-z)

Which indicates the blindingly obvious point that trafficking is not an appropriate z.

The event the variable z gives the probability of must be a yes or no event. Since trafficking is only yes/no on an individual basis (ie the level of trafficking is not yes or no), the model is suspect.

Reviewer’s probable advice to journal: Article not publishable without major revisions.

For more on migration, trafficking and the sex industry, visit Border Thinking.

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2 responses to “Trying to prove Swedish law reduces trafficking: Garbage in, garbage out”

  1. Per Olsson says:

    Thank you for your insightful and important blog post. No service to those who are trafficked against their wills with false numbers and statistics. All too often people try to support a good cause with absolute bullshit, which of course does exactly the opposite.

    Per Olsson
    http://www.frimobil.nu
    “Mobil upplåsning”

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