  Introduction: Two key dimensions of the mind are understanding and responding
to another's mental state (empathizing), and analysing lawful behaviour
(systemizing).
  Methods: Two questionnaires, the Systemizing Quotient (SQ) and the Empathy
Quotient (EQ), were administered to a normal control group and a group of
individuals with Asperger Syndrome (AS) or High-Functioning Autism (HFA). The
multivariate correlations of the joint scores were analysed using principal
components analysis.
  Results: The principal components were well-approximated by the sums and
differences of the SQ and EQ scores. The differences in the scores corresponded
to sex differences within the control group and also separated out the AS/HFA
group, which showed stronger systemizing than the control group, but
below-average empathy. The sums of the scores did not show sex differences, but
did distinguish the AS/HFA group.
  Conclusions: These tests reliably sex the brain, and their correlations show
that empathizing and systemizing are not independent, but compete neurally.
Their combined score (EQ + SQ) quantifies the deficit in autism spectrum
conditions.
