The truth behind the world's most reliable IQ test

IQ tests are available by the thousands online – but it can be difficult to know which ones are the most reliable.

And while it's nice to think you can take a quick IQ test and potentially discover that you’re actually a genius, people rarely question what it actually means - or how a set of questions can actually measure it.

Stanford psychologist Lewis Terman once explained IQ like this:

If a subject’s 'mental age' was the same as his or her physical age, their 'intelligence quotient,' or IQ, was defined as exactly 100.

If a subject lagged in mental age compared to physical age, the IQ was less than a hundred; if she was more mentally advanced, she was assigned an IQ above 100.

Unfortunately, the most comprehensive IQ test doesn’t actually exist, because they don’t really work.

Scientists have argued that intelligence cannot simply be measured by asking a few questions and assigning a score, as much as we would like it to.

Siddartha Mukherjee, Pulitzer Prize-winning author of The Gene: An Intimate History, explains:

Intelligence and temperament are not marathon races: there are no fixed criteria for success, no start or finish lines — and running sideways or backward, might secure victory.

In short, there's no objective measure of intelligence - it's a multifaceted thing.