Zener cards were developed and designed by Karl Zener, a Swiss Psychologist, and his associate J.B Rhine, at Duke University during the 1930's, to test an individual's psychic abilities or ESP (Extra Sensory Perception). Zener cards can test many types of psychic abilities including the ability to perceive objects or events that already exist or have occurred, but are not known to you (clairvoyance); your ability to see the future (precognition); and the ability to transfer thoughts or feelings via a medium other then the 5 senses (telepathy).



The deck consisted of 25 cards made up of 5 subsets of identical cards. The pictures on the 5 cards consisted of a cross, waved lines, a hollow circle, a hollow star, and a hollow square. The cards were originally made out of a flimsy material. This material was later determined to be biased due to its translucence which allowed individuals to see the shapes through the cards. So, subsequent decks utilized a thicker card stock to eliminate the bias and lend credibility to the statistical data.

The test for clairvoyance consisted of the person conducting the test, subject being tested, and third party witnesses. The experimenter shuffled the deck of cards then selected a card in the deck looked at it asked the subject what it was and recorded the data until the entire deck had been exhausted. In addition further controls were implemented as testing progressed including the use of partitions and separate rooms for the tester and subject. This ensured that the chance of cheating would be minimized.

The analysis of the tests outcome was based on pure statistics. As the deck was constructed of 5 different cards the overall probability of getting the correct answer by chance would be 1 in 5 or 20%. Several tests were conducted to approach a normal distribution and eliminate any significant chance for statistical anomalies to affect the results significantly. For example: on one test set an individual guesses 50% correct but on the next 6 test sets the individual averages 10% this would identify the first test as being anomalous and either thrown out or averaged in with the other six tests diminishing its statistical impact. For example the 6 runs at 10% would be 85.7% of the weight in the average and the 50% would be 14.3% of the average so 10 * .857=8.57 + 50*.143=7.15%= an avg. of 15.72% accuracy. To be considered to have ESP one would have to continually score higher than 25% on the Zener card test to be statistically significant.

In conclusion Zener and Rhine especially Rhine and his wife are considered to be the founders of modern day Para-Psychology and Karl Zener considered the inventor of the Zener cards which to this day are still used to test for psychic abilities.