Expected numbers of cancer were calculated as the sum of stratum-specific products of background cancer incidence and person-months at risk among the PWA and were discounted for periods before AIDS onset to account for reduced survival following a cancer diagnosis (Breslow and Day, 1987; Grulich et al, 1999; Frisch et al, 2000; Engels et al, 2003).
Total observed and expected counts were obtained by sum of the strata.
The degree of cloudiness is calculated as a weighted sum of each cloud strata for each day, and the global radiation is calculated for each location in the time step of one hour.
The resulting expected numbers of deaths were summed across strata to generate the expected number of deaths for each cause of death category and overall.
1 To correct for a possible sample selection issue, we reweight all of our observations by using the total sum of weights for each stratum in the CIS 3.5 based on the two criteria given in the text.
Then the model is 3 The conditional Poisson model is the same as model (3), except that instead of the parameters {αs} being estimated they are "conditioned out", by conditioning on the sum of events in each stratum.
In effect, such measures represent weighted averages of the associations, summing across strata in which the association with neurodevelopment is stronger and strata in which it is weaker.
Tests for the homogeneity of risk estimates across strata were based on a weighted sum of the squared deviations of the stratum-specific log-odds ratios from their weighted mean (Rothman and Greenland, 1998).
All calculations of expected and observed cancers (see below) were undertaken within these strata (i.e., they were based on people who were the same, in respect of age group, gender, etc) and were then summed across strata to give overall expected and observed cases of each cancer.
The standard approach in the Office of National Statistics is to pair off contiguous PSUs into collapsed strata, and to base the variance of the estimator on the squared differences between PSUs within strata, summed over strata.
