At one end of the scale, some forensic statisticians are employed by forensic science units specifically to analyse forensic data; at the other end, there are some researchers who specialise in carrying out statistical research on forensic matters and act as consultant forensic statisticians when required.
Researchers will, of course, be considering new ideas. Invariably, consultant forensic statisticians will use similar statistical analysis wherever where on this scale they are working but sometimes – occasionally – they will need to use more sophisticated methods of analysis.
To evaluate evidence appropriately, you need to compare probabilities of the evidence under two different propositions. These propositions are usually those put forward by the prosecution and the defence. There are advanced statistical methods for doing this (for readers who are technically inclined, they are based on likelihood ratios or Bayes’ factors). Much theoretical work has been done in the development of these methods. Calculations based on them might sometimes be fairly straightforward, though it also often turns out that there are non-standard issues to consider.
One example of casework that a forensic statistician may be involved with is DNA profiling, which is a powerful method of identification using genetics. Often, the evidence to be evaluated involves human (or sometimes animal) biological material such as blood, semen or vaginal fluid. Considerable work has been done in statistical and population genetics in assessing the importance of such evidence. Applications, however, are often not restricted to simple cases with one sample of DNA left at the scene of a crime and one suspect. Complications very often arise, for example because relatives may be involved, or the suspect may have been identified by a search through a DNA profile database, or the sample found at the crime scene may be a mixture of body fluids from more than one person. More advanced statistical methods are required in such situations.
Another role of a forensic statistician relates to sampling problems and determination of sample size. In some cases, it is necessary to examine a consignment of similar-looking items, and it is often not practical to examine every item. This may be purely on financial grounds but may be on health grounds also. The question then arises as to how many items should be examined on a sampling basis. For example, the consignment to be examined may be a set of CDs, some of which are thought to contain pornographic material. Then it is desirable for the examining officers to examine as few CDs as is commensurate with a good description of the proportion of the CDs which are illicit. The sample size determination is really just a quality control problem; there are UN Guidelines where the problem concerns drugs.
Finally, an important part of being a forensic statistician, as indeed it is for any statistician, is the ability to communicate results effectively to non-statisticians. Forensic statisticians may be required to attend court cases as “expert witnesses”. This involves reporting calculated probabilities, or other statistical measures, to the jury, and explaining to them how the calculations were performed. This is a challenge in itself, as the jury will typically consist of people who have little knowledge of statistical methods, and is further complicated by the need to choose careful wording (so as not to “lead” the jury into a decision on guilt or innocence of a defendant).
Take a look at our profile of forensic statistician Colin Aitken to learn more.
The main route into a career involving forensic statistics is essentially as an academic, either as a university lecturer or specifically as a researcher. You would probably need to gain a lecturing or research post in a mathematics or statistics university department, and then pursue a research or consultancy path as part of your day-to-day work there.
Continuing professional development
Forensic statisticians need to continue their personal and professional development. This can be done in several ways.
Most universities offer staff development programmes in which you may take short courses on almost anything, including computing software, presentational skills, management development and teaching skills. If you do not work in a university, there are likely to be courses of a similar nature available.
The statistical methods on which your work is based are also, of course, used in other application areas. You will probably find that there are conferences where the latest developments in these methods are explored; you might be able to submit papers or abstracts about your statistical work and attend these conferences, when you could have the opportunity to present your own papers as well as attend other presentations. Many conferences also have workshops in which you could participate.
These conferences could be in statistical, legal or forensic scientific areas. There is one specialist forensic statistics conference (the International Conference on Forensic Inference and Statistics) which is held every three years. In 2011 it was held in Seattle and in 2014 it will be held in the Hague.
You are also likely to be encouraged to write up the statistical aspects of your work as formal papers for academic journals. It’s important to develop your communication skills so that you can report your findings effectively to members of the police and legal professions, particularly if you actually appear in court as an expert witness. It will also be important to gain some understanding of the legal system.
Your professional work as a statistician might well make it appropriate for you to seek the professional qualification of Chartered Statistician (CStat), which would give you a professional affiliation with the Royal Statistical Society.
Work as a forensic statistician is likely to be on a consultancy basis, often coupled with a career as an academic. So there is, in effect, no salary structure attached to a career as a forensic statistician per se. General information about salaries in the academic sector can be found on our career as a university lecturer page. This also contains information about academic career structures and promotion prospects.
There is an increasing need for people to understand the role and application of probability and statistics in forensic science and the law. However, there are essentially no jobs and no career structure in forensic statistics in the UK as such.
The Forensic Science Service (FSS) of England and Wales has an Interpretation Group which considers problems of evidence evaluation, but it is small in size. In many cases, if the FSS wants help with a problem, it employs consultants. The Home Office has a Policing and Reducing Crime Unit which offers occasional contract work for statisticians to assist in particular projects. Individual police forces and law firms may also seek assistance with particular cases.
The area of DNA profiling is also growing. Although not strictly forensic statistics, there may be opportunities for statisticians in companies specialising in the analysis of DNA profiles for paternity and kinship testing.
Again, the absence of a career as such means that there are unlikely to be advertisements explicitly for “forensic statisticians” as such, though there may be opportunities for statisticians and programmers within government or commercial forensic science and DNA profiling organisations. Any advertisements might appear in several places, including the following:
- Daily newspapers (The Times, The Guardian and The Independent are probably the best).
- Electronic mailing lists (such as Allstat).
- New Scientist