Incidence of disability progression events by the evaluated criteria. The graphs show the observed mean incidence (black), the maximum hypothetical incidence given that sufficient follow-up time to enable confirmation of each event was available (grey) and the incidence of the progression events which were persistent at all subsequent time points (yellow). Mean and 95% CI (Poisson) are shown. The criteria were evaluated in a cohort consisting of 16 636 patients followed over 112 584 patient-years. Two EDSS progression strata were defined as increase in EDSS by 1 step if baseline EDSS was 5.5 or lower, or increase in EDSS by 0.5 otherwise. Three EDSS progression strata were defined as the increase of EDSS by 1.5 steps if baseline EDSS was 0, by 0.5 steps if baseline EDSS was above 5.5, and by 1 step otherwise.