From what I can tell, it is usually associated with a respiratory failure that is related to overheating (children that young can't regulate body temperature and many parents overdress their children, particularly indoors, when in fact you should never have your baby dressed more than you would feel comfortable in terms of feeling too hot) and air quality problems (smoking in the home sees SIDS spike). Basically, the likelihood is higher when the child is in a smoky, stuffy, overheated room without adequate and regular parental supervision, one reason SIDS hits lower-income groups with a statistically higher likelihood.