If the shaded areas are the 95% Confidence Intervals that tell us the range of possible values at each point in time, and if the way of measuring is the same over time, what else might account for the way that they widen?

Cumulative Incidence, % 2.5 2.0 1.5 1.0 0.5 0.0 00 T T T Vaccinated Not vaccinated 1 3 5 7 10 14 Age, y 235 016 Children at risk, n Vaccinated 3457 571 550 493 444 391259 Not vaccinated 654 004 66497 36343 27 392 18949 37 267 823 Cumulative incidences of autism (unadjusted and with 95% CI bands) in 657 461 children born