Venn Diagram for a Quadruple Risk Model of SIDS. These four probability factors involved with SIDS explain the age and gender distributions invariant with different sleep position, and subsets of SIDS found with and without neurological prematurity and respiratory infection. It is proposed that a prone infant is susceptible to SIDS anywhere in the intersection between the genetic (Pg) and anemia-related apnea (Pa) factors, but a supine sleeping infant is only susceptible to SIDS if it is in the intersection of all four factors (Pa, Pg, Pi, Pn).