Statistical Analysis
Statistical analyses were performed using RStudio version 1.2.1335
(RStudio, Inc). Patient characteristics and reoperation rates (event
rates) were compared using χ2 or Fischer’s Exact Test
where appropriate. Time-dependent comparison of reoperation-free
survival was demonstrated using Kaplan-Meier Survival curves with 95%
log-log confidence intervals. The survival curves were log-inverted to
demonstrate cumulative hazard of reoperation. The patient population was
analysed as a whole and in subgroups based on age, sex, and current
smoker status. A Cox-Proportionality Hazard Model comparing age, sex,
current smoker status, and valve brand, but no interactions, was
developed to determine Hazard Ratios of the variables. Competing risk
analysis due to patient mortality was not performed due to lack of
patient mortality data.