Alternate scales of childhood adversity measured as 0/1+, 0/1/2+ or 0/1/2/3+ exposures were considered. As there were no a priori expectations of the most appropriate scale for measuring environmental exposure and none of these measures offered significant improvement in the prediction of CD over scales using the full range of measure (0-5 exposures), each scale could be considered equally informative. Furthermore, a scale consisting of 0/1/2/3+ exposures increases the cell size of those exposed at the highest levels and minimizes loss of information that results from collapsing the scale. Therefore, the ordinal measure of childhood adversity using a scale of 0/1/2/3+ exposures was used. This measure was treated as a continuous variable to maintain model interpretability while attempting to address the issue of low frequency at the highest levels of exposure. Maternal ASP (measured as 0-5 symptoms) was treated in an identical manner and a scale of 0/1/2/3+ symptoms was used.
