as a simplification of a much larger
n-dimensional feature space. The two groups differ moderately on feature X
differ greatly on feature Y
and do not differ appreciably on feature Z; within-group variability on feature Z is much greater for the people with MDD than for those with PTSD. From a systems perspective
the mental health states of these people are emergent properties arising out of interactions of numerous biopsychosocial features (e.g.
social environments). Mental health states cluster to some degree because features stand in probabilistic relations to each other (e.g.
severe trauma often leads to nightmares). Superimposing diagnoses on this complex landscape leads to one person per group who is most typical of the diagnosis (black circles)
but also ignores meaningful interindividual differences. The diagram in (b) uses two copies of the same playing card
held between two fingers
as a model for vulnerable and resilient mental health states. The left card is in a vulnerable state and can be moved with little energy to an alternative state. The right card is in a resilient state
and forcing a phase transition to an alternative state requires considerable energy.