What was tested
The idea behind profiling is simple: use clues from a crime to describe the likely traits of the person who committed it. The method took shape in the second half of the twentieth century and quickly became well known through books and movies, but it was not tested until later.
In studies, specialists and ordinary people were given the same materials, and the accuracy of their descriptions was compared. Specialists did show an advantage, but it was small and did not appear in every study. The gap was far smaller than expected.
Classic psychological profiling: weakly supported
The second problem is the wording. Many descriptions contain statements that are true of almost everyone: withdrawn, has had relationship difficulties, probably lives alone. A description like this seems accurate in hindsight, once the person has already been found.
What does work
Guesses about character and biography, poorly tested and easily applied to many people
The geography of incidents and case linkage, tested with statistics
The geographic approach is based on a pattern: people act in familiar areas, but usually not right near home. The locations of incidents can help outline the likely area where someone lives, and these calculations can be tested against past cases.
The second useful tool is case linkage. It asks not "what kind of person did this?" but "were these incidents committed by the same person?" This is a question about matching features, not personality, and it can be tested.
Profiling also has a downside. An overly confident description narrows the search, and leads that do not fit it get dismissed. There are known cases where this sent investigations in the wrong direction for months.
It is also worth separating out the role of movies. The image of a specialist who can name a criminal's profession and marital status from a single detail comes from films and books, not reports. Expectations of the method took shape before it was tested.
The profilers themselves, incidentally, are usually more cautious than their reputation suggests. Their descriptions more often include probabilities and caveats, while the certainty is added when they are retold.
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Sources
- Reviews of research find only a small advantage for psychological profilers over comparison groups
- geographic methods and case linkage are tested against sets of solved cases