Attributable and avoidable burden. a = disease burden at T
0 attributable to prior exposure. The burden not attributable to risk factor of interest (light area) may be decreasing, constant, or increasing over time. The middle case is shown in the figure. b = disease burden at T
0 not attributable to the risk factor of interest (caused by other factors only). Dashed arrows represent the path of burden after a reduction at T
0. c = disease burden avoidable at T
with a 50% exposure reduction at T
0. d = remaining disease burden at T
after a 50% reduction in risk factor.