Journal of Biostatistics and Epidemiology 2016. 2(2):88-97.

Methods of competing risks analysis of time to occurrence of reflux among children with antenatal hydronephrosis
Maryam Nazemipour, Abdol-Mohammad Kajbafzadeh, Kazem Mohammad, Abbas Rahimi Foroushani, Maryam SeyedTabib, Ali Nazemipour, Mahmood Mahmoudi


Background & Aim: We aimed to describe a standard survival analysis, so that we can analyze some factors related to the time of occurrence of different types of reflux (unilateral-left, unilateralright, and bilateral) in children with antenatal hydronephrosis (ANH) and to provide an approach taking competing risks into account.
Methods & Materials: We used data of 193 children that was collected from Pediatric Urology Research Center of Children’s Hospital Medical Center, affiliated to Tehran University of Medical Sciences, Iran. The cause-specific and subdistribution hazard were computed. P < 0.05 was considered as statistically significant. R packages were used for analyzing the data.
Among these infants (36 girls, 157 boys), 117 (68%) cases had bilateral reflux as the event of interest. The variables “Sex” and “Direction of ANH (in bilateral level)” were significantly different (P<0.05), while “Severity of ANH (in moderate level)” and “Number of other kidney diseases beside ANH and vesicoureteral reflux (VUR)” were borderline. The cumulative incidence derived from the competing risks approach was at a lower level of estimate in comparison with the Kaplan-Meier method. The cumulative incidence curve depicted for the bilateral reflux in subgroups of the sex variable, confirmed the effect of sex.
In the competing risks framework, it is inappropriate to use the Cox and Kaplan-Meier methods, which do not take competing risks into account. Multivariate regression model like the subdistribution hazard model besides the cumulative incidence curve are recommended.


Competing risks; Cause-specific hazard; Cumulative incidence function; Antenatal hydronephrosis; Reflux

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