There are a number of factors which affect the accuracy of a Lie Detector test, so how accurate is it?
Some of these things can be controlled by the examiner, some of these cannot. The things that an examiner can control include being properly qualified, which involves training with a Polygraph school accredited by The American Polygraph Association (APA) and ensuring that they keep up to date with the latest research and any new developments. (Please note the APA does not accredit polygraph businesses, it is the individual examiner themselves who can be a member if they meet the APA’s criteria). The examiner also needs to be using the latest computerised polygraph equipment. The examiner must also conduct the examination in an appropriate environment suited for testing.
There are a number of things not within the control of the examiner and some that are within the control of the examinee.
First of all, the person taking the test should only be asked questions to which they are certain they are being truthful. A polygraph, despite commonly being known as a “lie detector” is actually verifying truthfulness. Essentially this means that any questions where doubts or uncertainty exist, or questions the examinee is unsure about or does not remember, means they are not being truthful – and you cannot be telling the truth if you do not remember! In our experience if the person taking a test is being asked questions about a time when they were very drunk or under the influence of drugs, this is likely to adversely affect the result.
It is irrelevant how accurate the test is – if the questions asked are not good polygraph questions for that person. So, it is vitally important only questions the examinee is 100% certain they are truthful to, should be asked.
Secondly the examinee also needs to follow the instructions they are given by the polygraph examiner during the examination process. Contrary to films and other fictional depictions of polygraph testing, there are no tricks or surprises. The examiner will explain everything in advance and the examinee will only be asked the questions which have been discussed during the pre-test process. If the examinee does not follow all the instructions given this is likely to adversely affect the outcome.
Additionally, it is the responsibility of the examinee to ensure they fully understand everything the examiner explains to them. There is a lot of information relayed during the pre-test process of the examination and it is important that the examinee understands what they have been told. This process cannot be rushed. If there is terminology used that the examinee does not understand then they need to tell the examiner. If there is something on their mind in relation to the issue which is bothering them, they should tell the examiner. On the basis that the examinee follows these instructions and examiner is utilising the most suitable technique (most accurate test for the particular circumstance), which is quite often a single issue test, then the test will be as accurate as it possibly can be. Maximum accuracy will not exceed the mid to high nineties (%). The APA is the organisation responsible for most of the polygraph research and they have conducted a meta-analysis which can be found on their website: American Polygraph Association Meta-Analysis On Accuracy