Hiring private detectives to investigate paranoid delusions

In 1684, the famous writer, Nathaniel Lee, was becoming increasingly disturbed and was promptly admitted to Bethlem Hospital. While protesting his sanity, he described the situation as one where 'they called me mad, and I called them mad, and damn them, they outvoted me.' Over three hundred years later, the difficulty of agreeing on whether someone's belief is a paranoid delusion, a sign of psychotic mental illness, is still troubling psychologists.

Delusions are broadly defined as false, fixed beliefs that are held despite obvious evidence to the contrary. Sometimes, it's a clear-cut case. If someone believes they are dead, a condition known as Cotard's Syndrome, you can be confident that the belief is a delusion. On other occasions (and these occasions are by far the most common) the question relies on a judgement of how well the evidence supports the person's belief. This is where it gets tricky, because what counts as evidence, and what counts as 'well supported' are often a matter of opinion.

Someone goes to a mental health professional and says 'I feel awful. I'm being targeted by my neighbours, and they've implanted microphones in my house to listen to my breathing.' It certainly sounds strange, and maybe they've already been diagnosed with a mental illness in the past, so we might just think it sounds unlikely enough to count as a delusion. But we know, for example, that people diagnosed with schizophrenia are much more likely to suffer violence and discrimination. Perhaps, some of the paranoia is driven by genuine persecution.

So here's the experiment. Everyone who walks into a mental health clinic is interviewed and their seemingly paranoid beliefs are noted. The mental health professional is asked to make a judgement on how delusional the belief might be. Then, each client is assigned a world-class private investigator, who is given the job of checking out all aspects of the belief, no matter how unusual. Is anyone in the neighbourhood persecuting the person? Are there really microphones in the house? Is there anyone who might have an interest in listening to their breathing patterns?

At the end, the professionals' judgements are compared to the evidence from the investigation, and we get to see how good we are at distinguishing paranoia from realistic concerns. Just as importantly, the study would indicate where the borderlands of paranoia lie, giving us a better understanding of how the mind exaggerates our fears. Further research could look precisely at how genuine threats spark, ignite and become inflamed by the cognitive distortions of psychosis.

The experiment, of course, will never be run. Even ignoring the practical difficulties, it's simply too intrusive and risks breaking client confidentiality. To do their job, the private investigators would have to ask questions which would give away personal details. Thankfully though, good mental health care focuses on psychological distress, no matter what causes it, but the issue raises the important question of how much we rely on guesswork to judge other people's reality.

About the author

Dr Vaughan Bell is a researcher and clinical psychologist in training at the Institute of Psychiatry. He writes daily at the Mind Hacks blog.