2.4 Statistical analysis
Descriptive statistics such as mean and standard deviation (SD) and range, were reported for continuous variables, and frequency (%) for categorical variables. Two group comparisons were conducted using Wilcoxon rank sum exact tests for continuous data and Fisher’s exact tests for categorical data. A Firth’s logistic regression model was used to determine biopsy variables associated with residual melanoma at the time of surgical excision. We employed a backward selection approach to create a parsimonious model and applied Firth’s logistic regression to mitigate bias in estimates, given the limited sample size. Kaplan-Meier progression-free survival curves and log-rank tests were used to evaluate ulceration and presence of tumor-infiltrating lymphocyte (TIL) status at biopsy. Multivariable Cox proportional hazards model in combination with backward elimination method on preselected variables, was used to determine variables associated with progression-free survival.