Zener Cards: How the ESP Card Test Works and How to Score It

Where the cards came from

The perceptual psychologist Karl Zener designed the symbols in the early 1930s for his colleague J. B. Rhine, who ran a parapsychology laboratory at Duke University in North Carolina. The simple shapes were chosen to be easy to name and equally likely, so a score could be compared with chance. Rhine used the term extrasensory perception, ESP, for the ability he was testing, and his 1934 book of that name brought the method to the public.

The cards spread through popular culture, from the opening scene of the film Ghostbusters to puzzles and toys, so the cards are familiar to many who have never heard how they began.

How to run the test at home

You need a second person, a deck of Zener cards (printable sets are easy to find) and a notepad. The aim is to see how your score compares with what guessing would give.

1. Shuffle the deck thoroughly and place it face down where the guesser cannot see it.
2. The sender turns over one card at a time, looks at it, and does not react or speak.
3. The guesser names a symbol each time, and the sender writes down both the guess and the card.
4. Do not tell the guesser whether each answer was right until all 25 are done.
5. Count the hits and compare the total with the table below.

What score would chance give you?

If every guess is a blind guess among five symbols, the expected score is five out of 25. Scores near it are the norm, and scores a little above it are common. The figures below are calculated for independent random guessing and are approximate.

Why one good run proves little

A single run of 25 is a small sample, and a run of eight or nine is unremarkable if you try the test a few times, or if several friends try it. Stopping when you have a good result, and not counting the bad ones, quietly makes any score look better than it is.

Honest testing means deciding the number of runs before you start and reporting all of them. A guesser who is told after each card whether they were right can also learn the order of a poorly shuffled deck, which is not a psychic effect.

What happened to the original results

Rhine reported results above chance, and critics soon pointed to weaknesses: cards whose backs or edges could be read, sloppy shuffling, the possibility of unconscious cues from the sender, and errors in recording scores. When procedures were tightened, the above-chance results faded.

In the decades since, researchers have tried again with better controls and have not produced a result that other labs can reliably reproduce. The reasonable reading is that the early effects came from the weaknesses in method, not from an ability, though individual believers remain free to draw other conclusions.