This weeks ask a Science blogger question is:

“If you could shake the public and make them understand one scientific idea, what would it be?”

Random sampling. If I want to know how many crimes there were in the country last year, you get a more accurate answer if you take a random sample of people and ask them than if you add up all the crimes recorded by the police. Now the crime rate in your sample might not be exactly the same as the population, so you have introduced an error by sampling, but we can mathematically estimate the size of the error, while using police records introduces an error of unknown size — we miss all the crime that aren’t recorded. Alas, too many people don’t understand this. They can’t tell the difference between dodgy Internet surveys where the sample isn’t random, and surveys that use proper random sampling. My first post on this theme was in October 2002 which was before I started blogging. And in eighty odd posts on the Lancet study, the most common errors made by critics were because they just didn’t get random sampling

The round up of answers to last week’s ask a Science blogger is here.