Postdiction

Other Terms and/or Related Concepts

Hindsight Bias; 20/20 Hindsight

Description

The advocate claims that they accurately predicted an event after the fact, when in fact they did not, or can provide no evidence that they did.

Example

In her end of year wrap up column, financial astrologer May Kidup explains why the Leewoman Sisters Bank collapsed earlier in the year. She explains that it was written in the stars:

Sure, some like to blame the bank for overstretching itself, or the government for poor fiscal policy and a lack of regulation. But when you read the stars the true culprit becomes clear - a clash in the Pontiac, between Sami and Leroy. As we know, the sun is the father of the astrological Pontiac, and is represented by Leroy the Ladybug. Sami, the Queen Bee, is his son.

And as with all fathers and sons, when the son grows up he needs to show his father that he is a man. This happens when they are sitting in the same house. As such, they fight. This creates danger in the stock-market. That’s why the Leewomen Sisters Bank fell.

Comment

May Kidup claimed the cause of the collapse of the Leewoman Sisters bank was due to trouble caused by the astrological fighting of Sami and Leroy. The problem is, besides the astrological Gibberish, when an explanation comes after the fact, how can we verify or falsify it? In science, we would run the experiment again, or seek to make a prediction using the same model, that can be tested against a future event.

Astrology seems to go out of its way to avoid such empiricism. We would also ask for a much more explicit claim as a prediction. We would not be very impressed with a prediction that: “Sometime during the year, a bank will collapse”. We might think a claim such as: “When Sami and Leroy clash, the Leewoman Sisters bank will collapse”, is far more impressive. It provides us with enough precision as to be able to categorically say the event did or did not occur.

Such specificity in a prediction from an astrologer is unlikely. When going over an astrologer’s predictions for any given year – one finds they tend to be very general. There are occasions when they do get specific, often to do with deaths and divorces of celebrities. On reviewing such precise predictions, one finds a lack of hits (not that astrologers ever self-review...).

Other examples

Parents who claim, after their child was born, that they “just knew it was a boy (or girl)”. If they were to write down their guess before the child was born, at least we could confirm their claim of accurate prediction. Chances are many of these claims would turn out to are right (about 50%...) But if the claim of an accurate prediction is based on a memory, that is, they claim a successful prediction after the fact, then we cannot rule out postdiction. The greater number of times they claim this has occurred, without writing it down before the sex of the child is known, the more suspicious we should be. A charge of postdiction becomes more justifiable.