What is a logworth statistic, and how useful is it?
logworth is a p-value transformation based on Pearson Chi-Squared test. 

Pearson Chi-Squared test evaluates the probability of having a split caused by chance. The higher the Pearson Chi-Squared value, the higher the chance that the split is caused by dependence. A p-value is given according to the Chi-Squared score and the degree of freedom. 

Because some data can have high dependence relationship, the p-value can be extremely small. Taking a logworth of p-value (-log(p-value)) allows us to mitigate this extremely low value.