The ratio of the number of positive
fatal factors to the number of possible fatal factors in the same case was calculated as the abundance ratio, which
was used because information regarding all eight factors was not retrievable for all the patients at the time of
registration. The patient group was divided into four quartiles based on this abundance ratio, and the mortality
rate in each quartile was compared with the overall mortality rate among the 130 patients with AFE enrolled
between 1992 and 2006. The validity of this approach was confirmed in another dataset from a cohort of 38
patients with AFE in 2007.