Polygraph test, lie detector test validity & reliability
What is the reliability, validity of a polygraph test? Certainly, one the most asked questions when it comes to polygraph testing.
Although the question is straightforward, the answer is a little bit more complicated, but we will try to explain the difference.
Reliability of a polygraph test
When we talk about reliability of a polygraph test, we refer to the statistical probability that a given test structure will have the same outcome when applied to different people.
So, what is the probability that a truthful, deceitful person will be rightfully diagnosed during a polygraph test.
To be able to arrive to this conclusion different laboratory studies have been carried out, using different polygraph techniques. So, when we talk about reliability of a polygraph test we talk about the reliability obtained during these studies.
It is therefore important that we make the difference between the reliability of the instrument itself and the use of the instrument to obtain a qualified diagnosis about someone’s emotions.
Validity of a polygraph test
Now, is it valid to say that a polygraph instrument can effectively detect deception? Is it valid to say that the diagnosis can detect deception or truthfulness? Well, that is a different question?
To be able to arrive to such a conclusion a polygraph expert needs once again to apply techniques that are designed to diagnose somebody’s honesty towards a specific issue.
It is therefore paramount that the adequate techniques are used, applying the conditions that have been tested in laboratory to be able to ascertain such a diagnosis.
Polygraph as a forensic tool
Using the polygraph as a forensic investigation tool is possible and actually used on a daily basis by different police departments all over the world.
However, it is important that the right techniques and methodologies are applied.
The popular idea, that a polygraph test is connecting somebody to an instrument and asking random questions does not correspond to the reality of a professional polygraph exam.
It is therefore important that the polygraph expert understands the issue to be solved so that he or she can apply the right and validated polygraph technique.
For a better understanding of the validity studies please check ASTM or APA.