Risk interval | Duration since starting observation | Duration since starting observation | Duration since starting observation | Duration since previous injury |
Risk set for injury k attime t | Independent injuries (any given injury occurrence is not affected by previous injuries) | A random effect (or frailty) term is used to account for the within-player correlation between injuries to enable modelling of the phenomenon by which some players are intrinsically more or less susceptible to experiencing a given injury than others are | All players who have not experienced injury k at time t | All players who have experienced injury k−1, and have not experienced injury k at time t |
Baseline hazard | Common/same baseline hazard across all injuries | Heterogeneity is directly incorporated via a random effect so that the baseline hazard is allowed to vary with each injury | Common baseline hazard for all injuries within a player | Stratifies the data by injury so that the baseline hazard is allowed to vary with each injury |
Within-person correlation | The within-person injuries are independent | Captures within-person correlation due to both injury dependence and heterogeneity | The within-person injuries are independent | The current injury is unaffected by earlier injuries that occurred to the player |
Comment | A-G model is recommended when there is no injury dependence and no covariate/injury effects | The frailty approach accounts for heterogeneity. The random effect (the frailty) has a multiplicative effect on the baseline hazard function and the mixture of individuals with different injury risks | At any time point (matches), WLW-TT describes all players who have not yet experienced k injuries are assumed to be at risk for the kth injury which is not realistic in the sports setting injury data | PWP-GT model takes into account the ordering of events |