Editor’s Note (28 December 2016): Through the end of the year, BBC Capital is bringing back some of your favourite stories from 2016.

Don’t do an IQ test after a full week’s work if you are 40 years or older. You could be disappointed.

If you’re over 40, working more than 25 hours of work a week could be impairing your intelligence, according to a study released in February by researchers for the Melbourne Institute of Applied Economic and Social Research in Australia. The team conducted reading, pattern and memory tests in more than 6,000 workers aged over 40, to see how the number of hours worked each week affects a person’s cognitive ability.