What I said in my comment above is misleading. If they had found an effect, it would have meant something, although they would have again stated it as stronger than it really was: "For all children, food dye affects behavior." There could in fact have been one food dye monster child whose behavior was radically altered by food dye. Having failed to find an effect, they can conclude that they failed to find an effect on all children, which is still useful information but in practice would be very difficult to use correctly.