The most common mistake in interpreting research is confusing correlation with c

The most common mistake in interpreting research is confusing correlation with causation.  A correlation shows that two variables are related.  However, it does not prove that one variable causes the other.

Dangerous conclusions can be drawn because people misunderstand this, as in the case of vaccinations and autism. 

What is the correlation between vaccinations and autism? Why do many parents see this correlation and believe that it proves causation.