Results analyzed by the Cox proportional hazards regression on roots of L. chinensis in relation to treatment, soil depth and time of root birth respectively.

Hazard ratios for different categorical covariates are the mortal risk relative to a reference level, given for each covariate in the left-hand column. A negative parameter indicates that increases in the covariate would result in decreases in the mortal risk, while a positive parameter indicates the opposite trend. Confidence intervals of 95% are upper and lower limits. P