Is handwriting really accurate in identifying people?

There was a well-known article in a law journal in 1989, debunking the notion that a handwritten signature uniquely identifies the person who signs the document (Risinger, Denbeaux and Saks, 1989)

http://law.shu.edu/faculty/fulltime_faculty/risingmi/137UPaLRev731.pdf

A valuable introduction to this topic written much later can be found in

http://www2.warwick.ac.uk/fac/arts/ren/publications/lima/handwriting/forensic/

This latter article describes the safeguards prescribed by the US Supreme Court while evaluating the evidence given by Handwriting Experts. It also refers to a paper which gives the results of one study showing 7% errors in the case of experts and thirty eight percent in the case of non-experts. Note that people can be sent to jail ( or worse!) on the basis of testimony from "handwriting experts", or that your parents' property can go to someone else because of a disputed signature on a Will. I find 7% error rate among the experts very shocking. That is why we need to do more research and discuss this issue more in public.

But there is a widespread "conspiracy" to act as if this assumption need not be questioned. A lot of crime takes place in the world because this assumption is not correct. However, there are very few scientific publications that have tested this assumption. Can you think of a short research proposal saying how you can test this assumption? It would be excellent if you plan to do this research systematically and publish the result in a journal (printed journal or an online one). You might credit in school or college for doing this research. Further a teacher/advisor can guide you into planning the work to avoid weaknesses (experimental design).

The article I mentioned above says that handwriting verification of an individual is about as accurate as reading tea leaves to tell the future.

P. S. Please note there are two questions either of which you can address:

1. If a given signature is that of a known person whose sample signature is available? Yes or no?
This is relevant for instance when a bank verifies your signature on a check (cheque) to see
if it matches a "specimen signature" which you gave them while opening the account.

2. Given a signature is that of one of 30 people in a group, and given their sample signatures,
can you find out who the signatory is?
This is relevant for instance when the police try to identify a person out of a set of
suspects on the basis of a handwritten signature on a letter.
An additional question is if the identification works better when a whole handwritten letter
is available for comparison with handwriting on the supect's diary.

Suggestions:

a) Three relevant ideas are:

i) False positives: Cases in which the process being used identifies a signature as the one we
are looking for, while in fact it is not. This happens when the bank recognizes a forged
check as the real one!

ii) False negatives: Occurs for instnace when the bank refuses to pay against your
check saying the signature does not match the speciiimen signature.

iii) When you use comparison of handwriting to identify a criminal, how sure are you of the
result? 90%, OR 99%? or only 70%?

a) Avoid violating the law by forging someone else's signature as a part of the experiment. Think out how you can do something lawful, which allows you to test the hypothesis.

b) An experiment like this should involve at least 30 individuals to ensure that the result you get can be verified by someone else who repeats your published experiment with another group of volunteers.

c) It is not only the first publication that gets credit. A few following ones which test the repeatability of the finding will also be widely cited in future.

Have fun trying this out, and become the author of a research paper. As you know, they respect such things when they consider you for admission in college. Who knows, you might land up in Law School because of this work.

I hope teachers of statistics and experiment design would encourage their students to
try out these ideas.

Srinivasan Ramani