By the way, re someone's reference to much emotion affecting parents' decision on MMR and "risk" of autism being lower than "risk" of catching measles, mumps, rubella:
That risk assessment tells me that some people here are confusing risk and probability.
Probability = The likelihood of an event occurring
Risk = Probability x Impact of an event
Take Russian Roulette.
Probability of getting the bullet = 1/6 = 17% (low)
Risk = Enormous. 1/6 x certain death (very high)
Coming back to MMR example:
Probability of catching m, m, or r: let's say 80%.
Risk = 80% x a childhood illness (a week of illness, but nothing major, as long as you take DC to hospital at first sign of anything unexpected)
Probability of autism = very low, let's say 0.1%.
Risk = Enormous. 0.1% x losing your child (mentally), irreversibly.
Therefore, while probability of catching measles, mumps, and rubella is certainly lower than one's child regressing into autism, risk of the latter is much higher.
Mums have an instinctive understanding of the above (that no illness is worth chancing autism, no matter how small the possibility) but can't explain it and hence are branded "emotional" in their decision. It isn't so.