Parents will think the risks of vaccination are much higher after reading testimonials from parents whose children had negative reactions, in spite of having seen statistical information that says the risks are low.

CNN: Talk back to your doctor

"The additional risk is quite small and will probably be hidden by the noise of other (cancer) risks like people's lifestyle choices and statistical fluctuations, " he said.

NPR: WHO: Small Cancer Risk After Fukushima Accident

When researchers question people about their expectations and compare them with harsh statistical facts, it turns out that we tend to underestimate darker risks, such as dying prematurely or suffering financial setbacks.

FORBES: The Pitfalls Of Perception