PhD thesis - University of Hertfordshire Research Archive

compare the period after 2000 with previous years, as a rule change on the
recording of pneumonia as an underlying cause was introduced at this time.
A categorical variable was created to represent approximations of the
seasons in which death occurred (Winter=December to February;
Spring=March to May; Summer=June to August; Autumn=September to
November). The effect of each explanatory variable on the outcome of
interest was assessed using single variable logistic regression. Variables
significantly associated with the outcome of interest at a level of 90% or
higher were included in a multivariate logistic regression model, which was
simplified subsequently using the likelihood ratio test with a P value cut-off of
0.05.
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