This graph demonstrates that SIDS does not have any medical cause.
Excerpted from T. J. Sprott, The Cot Death Cover-Up?, Penguin Books 1996 pp64-65:
This graph, developed originally by Peter Mitchell, is arguably the most important piece of epidemiology relating to the cause of cot death [crib death, SIDS]. The range of cot death [crib death, SIDS] risk from the lowest group (first babies of wealthy parents) to the highest group (babies of unmarried mothers) is 1:22.
This data is part of the overwhelming proof there is only one cause of cot death [crib death, SIDS] and destroys any argument that cot death [crib death, SIDS] has a medical cause.
The more babies that use a mattress the greater is the risk of SIDS.
This accounts for the higher cot death [crib death, SIDS] rates in less well-off families, who are more likely to use second-hand mattresses. If a mattress contains the dangerous elements, and the fungus has become established in the mattress during prior use, the output of toxic gas commences sooner and is greater in volume.