Criminal Psychology: What are the Limits of Psychological Profiling?

   Sorry I've been gone for a while but I'm back with an excursion into the world of criminal psychology, much beloved by crime writes (Poirot for example, was basically a very good criminal psychologist). The idea of psychological profiling has always intrigued me, being able to massively reduce the suspects for a crime by deducing the personality and habits of the perpetrator would be an invaluable tool in forensics.

   The first thing to remember however is that a psychological profile can never be used as proof, only as a technique to gain hard evidence. This is because psychological profiling, even by the standards of forensic science, is a very young field with very few standardised methodologies, and even less scientific reliability. this makes the use of a profile as evidence usually a violation of rule 702 of the Federal Rules of Evidence.  Rule 702 states that expert testimony can only be allowed in court when:
 1) the testimony is based on sufficient facts or data
 2) the testimony is the product of reliable principles and methods
 3) the witness has applied the principles and methods reliably to the facts of the case.
   As such there are very few cases where you'd be able to convict on the basis of a criminal profile no matter how well you suspect fits it.

   Even with this caveat, criminal profiling is far from perfect. In fact for a scientific field it's positively riddled with problems. The main problem comes from the fact that the only standardised method of psychological profiling was created by Ressler and Douglas, who were commissioned by the FBI. They interviewed 36 serial killers who had been caught and imprisoned to draw up a list of statistics for the 'average' serial killer. There are several problems with this technique:
   1) The data pool is absurdly small, which leads to large confidence intervals and an inaccurate data pool to draw conclusions from.
   2) The tested group leaves out n important demographic, serial killers who haven't been caught. The 'type' of serial killer who manages to avoid capture (the one where profiling would probably be more needed) is totally absent from the data.
   These inaccuracies can lead to serious mistakes on behalf of the criminal profiler, which could be potentially lead to false convictions or releases if they were taken as hard evidence. For example, there was a case in 2002,of the Washington D.C. snipers, where the killer was predicted to be a white male working alone and turned out to be a father-son duo of black men. "Woops" would be an understatement.

   However there are upsides and success stories. First thing's first, Ressler and Douglas's experiment is ongoing, as the FBI interview more and more serial killers, expanding the pool and aiding with half the problems mentioned above. Psychological profiling can also be used to discover serial killers by linking cases, and showing there is a common killer, and there must be a reason that the FBI continues to fund it.

   Overall Criminal Psychology, while being a useful tool, should never be viewed as hard evidence and regardless of validity will almost always bias the jury. Despite all the criticism listed I believe science gives us the final word in the form of a study by Kocsis which showed that, in detecting criminals, criminal psychologists did have an almost 20% higher validity rate than the closest group, students (72 to 59%). Always consider psychological 'evidence' and always take it with a grain of salt. As always thanks for reading, over and out.