MODELLING SURVIVAL DATA OF THALASSAEMIA PATIENTS IN PAKISTAN
Abstract
Background: Fatimid Foundation with its centers serves as a charitable organization for millionsof blood disease carriers in Pakistan. This retrospective survival study is an analysis of the
Thalassaemia patients registered in Multan centre who are followed up to nine years to assess the
gender risk of death. Methods: Data on 120 patients of Thalassaemia during 1994-2002 was
analyzed. The standard Kaplan-Meier and Nelson-Aalen procedures were used to compare the
survival function of the male and female patients of Thalassaemia. The statistical significance was
also assessed using log rank test. The Cox Proportional Hazards (PH) model using a forward
selection procedure was used to identify the potential factors associated with the increase risk of
death. Results: By ignoring the censoring, the average survival time of males and females were
calculated to be 1308.1 and 1574.7 days respectively. The average hazard rate for the female
group was 0.00033 and for the male group it was 0.00061. The median survival time was
estimated from the Kaplan-Meier survival curves (Males: 1400 days, Females: 1785 days). Under
the censoring mechanism, the mean survival time for males was calculated to be 1465.82 days
with standard error of 146 days, where as for females it was calculated to be 1855.26 with
standard error of 151.82 days. When considering death as event of interest Under the Cox
modelling approach, we found a male patient of Thalassaemia was 1.484 times more likely to die
when compared to his female counterpart. When considering the iron over load as the event of
interest, we found a male patient of Thalassaemia was 1.753 fold more likely to reach excessive
Haemochromatosis level compared to female patient. Conclusion: The analysis reinforces that
female group prognosis is better than the male group. Further, our analysis of real survival data set
shows that the high status of Haemochromatosis level is associated with the increased risk of death
in patients with Thalassaemia with other possible confounders.
Keywords: Censoring; Cox PH model, Kaplan-Meier estimator, Nelson-Aalen estimator, Thalassaemia
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