I'm using the well-known USC Burns Survival dataset to explore logistic regression in R.
The independent variable is burn area, and the outcome is binary survival (yes/no).
In the documentation, burn areas are grouped as the 'midpoint of set intervals', and taken as a log ie.
log(area + 1)
for sample datapoints like (highest/lowest):
1.35 yes 2.35 no
Medically, burns are usually specifed in terms of surface area % of total body eg. 40%, or alternatively, as an estimate of surface area in square meters. My question is: how does this relate to the dataset independent variable ie. what does '1.35' actually mean in terms of % body surface area burnt? What would eg. 30% burns become in the dataset, using the 'midpoint of set interval'?