Schizophrenia and IQ

A question that comes up sometimes is whether or not there is a relationship between schizophrenia and IQ.  IQ stands for “intelligence quotient” and is a normalize measure of intelligence in relation to the rest of society.  People are fond of saying that brilliance is close to madness.  Many true geniuses appear very strange to everyone else who isn’t three and four standard deviations above the average IQ of 100.  So the question is… is there a link between IQ and schizophrenia?

 The Answer is Yes

Yes, there is a relationship at play here.  Of course, we can’t draw any conclusions about causation because we are looking at correlative data, but there does seem to exist a relationship between the manifestation of schizophrenia and someone’s measure on the intelligence quotient scale.  So is it a positive correlation, meaning that the appearance of schizophrenia is related to a higher IQ, or is it a negative correlation relating it to a lower IQ?

In 1984 (a twenty year old study at the time of this writing), researchers Aylward, Walker, and Bettes from the Department of Human Development and Family Studies at Cornell University performed a meta-study concerning this question.  A meta-study means that they didn’t conduct any experiments of their own, but that they compiled the data and conclusions from all of the related studies and performed a statistical analysis on them to draw a more final conclusion with greater confidence.

The Cornell Meta-Study on Schizophrenia and IQ Correlation

Without digging into this study at a depth inappropriate for this article, we can just discuss the conclusions as reported in the abstract of the study.  Unlike what the common sayings report, genius may appear like madness but madness is certainly not always genius.  In fact, concerning early-onset and adult-onset of schizophrenia, both groups experience on average intellectual decline and deficits over their lifetimes.

It is also reported that children and adolescents, those too young to be diagnosed but that are obviously preschizophrenic also perform at lower levels on standardized measures of intellect, including the Stanford-Benet IQ test.  We can only look at the data and report that without bringing opinion into the matter during scientific research, but we can all see that performance on a test while sick and distracted by symptoms doesn’t necessarily mean that a person is any less intelligent.  Just like some people have test-taking anxiety and perform worse for that reason.  These IQ deficits only increase as the onset continues and symptoms increase in severity.

Schizophrenia and IQ – Causation and Correlation

To reiterate the importance of not drawing a conclusion about causality, let’s consider this.  Another important question to be considered is whether the intellectual deficit is caused by schizophrenia, or whether it is a symptom of schizophrenia, which is to say that it is caused by schizophrenia.  With the current data and the uncertain neurobiological mechanisms by which schizophrenia is produced, we cannot draw this conclusion.  We can only talk about the relationship between IQ and schizophrenia, but we aren’t sure if one creates the other.

More studies have been performed since 1984 which further correlate schizophrenia with a declining IQ, however one study is a bit more important.  We know that intelligence is influenced by genetic factors and so is schizophrenia.  It was found through research by The Zucker Hillside Hospital and Harvard Partners Center for Genetics and Genomics in Boston that the dysbindin-1 gene (also referred to as DTNBP1) has an effect upon the risk of developing schizophrenia but also upon the general intellect.  A gene that effects cognitive ability and schizophrenia both is a great clue for us to unravel this mystery, but we still can draw no causation conclusions.


In time, we will figure out this relationship in more depth and understand why it exists.  At this point, unlike the idea that genius and madness are close to one another, the research is drawing a different picture, which is that schizophrenia and IQ are related, but in a negatively correlated fashion.  The presence of schizophrenia is related to a lower performance on standardized IQ tests.