<2500 g) and gestational age (mean, % <37 weeks, % <28 weeks) for each location, year, and sex. Second, we evaluated all microdata where both gestational age and birthweight were available and found a high degree of consistency in the correlation between them. Third, we took the pooled correlation coefficient from step 2 combined with univariate ensemble distributions from step 1 and used a copula linking function to simulate the joint distribution which was then summarised into each 500 g per 2 week category. Joint PAF calculation used a TMREL defined as the lowest overall risk of the entire matrix of birthweight and gestational age (see appendix 1 p 77 for more details).
