The Times Online’s David Aaronovitch, for whom “bad stats” is an obsession, lists three recently reported facts and explains why they are bogus.
One of these is a poll conducted by a union, Britain’s Teachers and Lecturers Association. They found very high rates of assault against teachers and abuse of teachers. They sent out questions to their members and closed polling after they got a thousand responses. The problem with that? Well, first, there’s self-selection bias (only those with a vested interest in the topic will respond), and second, people who answered quickly are likely to have stronger opinions than those who take their time.
Other false facts covered are the date of the Shroud of Turin (it’s still a medieval fake, no matter what you hear) and the estimated number of sex workers in Britain.
From the James of London in comments (at the times article):
My favourite has to be the one about Spinach being rich in iron. Someone put the decimal point in the wrong place when publishing research and increased the iron count by a factor of 10 and it has been accepted as “fact” ever since. That was in 1870.
Unfortunately, “James” himself is the one who is misinformed. He has uncritically accepted a factoid that is just wrong: spinach is high in iron. see here for example.