The Hazards of Self-Diagnosis

Flickr picture by The Doctr

A few weeks ago, I talked about why it wasn't the best idea to give yourself the Autism Quotient and act based on the results of the test.  The Autism Quotient is not meant to be a diagnostic test and, even if you get a high score on the test, you are still fairly unlikely to have autism.

But, for the sake of discussion, lets say that you do have a history of having some autism-like symptoms and decide to take the test.

If you get a high score on the test you might believe that, based the test result and your life experiences, it is likely that you have a form of autism.  After all, you are an intelligent, mature person who has carefully done research and made honest self-appraisals.  And the AQ test bears out your idea, so what could be wrong?

Well, to start off with, you might have schizophrenia, not autism.  According to a study¹ published earlier this week (open access, go read it) -

In clinical practice, differential diagnosis of high-functioning autistic spectrum disorder (ASD) and schizophrenia (SCH) is difficult but important. It is especially difficult when adult patients with ASD have psychotic symptoms as a result of maladjustment to their circumstances. Diagnosis of ASD requires a knowledge of early developmental history, but sometimes that is difficult to clearly ascertain when the patient is an adult. If such patients were not diagnosed as having ASD during their childhood, we cannot distinguish their symptoms from the positive symptoms of SCH. Similarly, when ASD patients are in social withdrawal or in an autistic state, it is difficult to distinguish their state from the negative symptoms of SCH. Thus, a reliable measurement for differentiating the two disorders is needed.

This study looked specifically at the Autism Quotient (AQ) test and how well it could distinguish between high-functioning autism and schizophrenia in adults.  The researchers gave the AQ to 51 adults of normal intelligence who had either autism or pdd-nos and 46 adults who had schizophrenia.

The main result was not too surprising.  The autism group, as a whole, scored higher on the AQ than the schizophrenia group. But - and this is the important bit - the AQ misclassified 8 (17%) out of the 46 patients who had schizophrenia as having autism.  As the researchers say in their discussion section, "high AQ patients with SCH cannot be distinguished from ASD by using only the scores of the total AQ and its subscales".

Let me put this another way.

The AQ can't reliably tell the difference between schizophrenia and high functioning autism.  Trained clinicians - people who do this everyday as part of their job - have a hard time as well.  So what do you think the chances are that an untrained person, researching the condition on their own, is going to be able to tell the difference?

Now, before you think this doesn't matter, consider that schizophrenia is known to be more common in adults that autism is.  The current figure for schizophrenia is about 1 in 90, or about 1.1% of adults over the age of 18.  The rate for autism in adults is not well understood but is, by most accounts, much lower than 1%.  I think it would be safe to say that, even if we were to be highly optimistic about how many adults have autism, there are going to be 3 adults with schizophrenia for every 1 with autism.

So, assume that you had a group of 1,000 adults where you had 4 adults (1 in 250) that had autism and 11 that had schizophrenia, and that you gave them the AQ.  Based on what we know about the AQ, we would expect about 25 of the group to score in the autism range.  Out of that group, most (20) would be misidentified, 3 would have autism, and 2 would have schizophrenia.

Or in simple terms, if the AQ gives you a high score and it is picking up on something that is really there, you have almost a 40% chance of having schizophrenia instead of autism.  That little fact might be important as schizophrenia is more easily treated than autism is.

All of this is just one small example of how a self-diagnosis could go wrong.  There are many other ways that the process can go wrong.  The bottom line is, if you think you have a problem, don't self-diagnosis.  Go talk to a professional who knows what they are doing.

References
1. Naito, Kenichi, Yusuke Matsui, Kiyoshi Maeda, and Kiwamu Tanaka. 2010. “Evaluation of the Validity of the Autism Spectrum Quotient (AQ) in Differentiating High-Functioning Autistic Spectrum Disorder from Schizophrenia.” The Kobe journal of medical sciences 56:E116-24. http://www.ncbi.nlm.nih.gov/pubmed/21063152.