The calculator is based on the BMJOpen paper Bed sharing when parents do not smoke, which uses data from five SIDS case control studies. It's an attempt to summarize the affects and interactions of risk factors covered in the paper, although very high and low results output by the calculator should almost certainly not be trusted.
The calculator inputs are taken from the variables in the study (tables 1 and 4). An initial mortality rate is taken from table 4 based on inputs related to the parents' alcohol and smoking habits, whether the infant is breastfed or bottlefed, and whether the parents room share or bed share with the infant (from the paper, these are variables that likely interact). The mortality rate is then multiplied by the AOR values of the other variables (in table 1) which are assumed to not interact. The default risk factor values in the calculator were chosen so that the default calculated mortality rate is roughly equal to the current annual SIDS mortality rate of 34 per 100,000 (and also based on the description of assumptions in table 4).
The weekly mortality rate graph data is taken from figure 1 in the paper and multipled by the calculated risk multiplier (resulting from the calculator inputs). It's likely that some risk factors would change the distribution and shape of the graph. For example, tables 2 and 3 shows AORs that change between weeks 2, 10, and 20. For now, the graph is scaled uniformly for the calculated risk. The first year risk is the sum of weekly risk values from the graph (e.g. 34 per 100,000 with default risk factor values selected).
SIDS mortality odds compared to the odds of other childhood events.