What an intelligence test is really doing
Proper intelligence testing began with Alfred Binet in Paris in 1905, commissioned to spot schoolchildren who needed extra help, and Binet himself warned against treating the resulting number as a fixed quantity stamped on a person. Modern batteries such as the Wechsler scales sample several narrow abilities, among them vocabulary, working memory, processing speed and matrix reasoning, then report a composite standardised so the population average lands on 100. The scores correlate with school and work outcomes well enough to be useful and loosely enough that no single figure sums anybody up. It takes an hour or two, in a quiet room, with a trained examiner sitting opposite you.
Memory and speed, which are stranger than they look
Two of the things these nine quizzes poke at have genuinely interesting science behind them. Working memory is the small, noisy workspace where you keep a phone number alive while hunting for a pen, and its capacity is tiny; George Miller's celebrated seven plus or minus two has since been revised downwards once researchers accounted for how we bundle items together. Reaction time is simpler and odder still. It slows gradually from the early twenties onward and swings with sleep, caffeine and the hour of the day, which is why laboratories care about differences of a few hundred milliseconds. Almost none of that survives contact with a web page, where your connection, your thumb and whatever is happening in the next room matter more than your neurons do.
On the percentages in the titles
Several titles on this page mention two per cent, three per cent, elite scores and rare common sense. Those are figures of speech rather than statistics. Nobody has normed these questions on a representative sample, and none of them is a validated instrument in any sense a psychometrician would sign off. What they are is good fun: a well-built riddle rewards the same slow, suspicious reading that a decent puzzle book does, and getting caught by a logic trap is its own small education. Claim the bragging rights, then hold the number very lightly.
