Feb29

How the Bayes Theorem Influenced A modern Day Assassin

Posted by Clint Reeves

Bayes Theorem

The formula above may well be saving the life of your computer every day, by quietly filtering and eliminating something we all loathe: SPAM.

It’s an example of the famed Bayes Theorem or Rule, which underpins the programming logic of modern day anti-spam software such as SpamAssassin offered by Midphase.

By the way, you can even request a more advanced configuration of Spam Assassin known as Spamalizer, which usesadvanced heuristics? to identify and block email spam.

According to the Economist, the Bayes Theorem was developed by the Reverend Thomas Bayes in the 18th Century and now influences scientific fields ranging from archeology to computing (and of course, spam filtering).? Just like Einstein used his thought experiments to formulate his Theory of Relativity, Bayes had to use his imagination (and not technology) to formulate how new evidence can change our beliefs about the world around us.

To understand how he did this consider this example quoted from the Economist:

Imagine that a precocious newborn observes his first sunset, and wonders whether the sun will rise again or not. He assigns equal prior probabilities to both possible outcomes, and represents this by placing one white and one black marble into a bag. The following day, when the sun rises, the child places another white marble in the bag. The probability that a marble plucked randomly from the bag will be white (i.e., the child’s degree of belief in future sunrises) has thus gone from a half to two-thirds. After sunrise the next day, the child adds another white marble, and the probability (and thus the degree of belief) goes from two-thirds to three-quarters. And so on. Gradually, the initial belief that the sun is just as likely as not to rise each morning is modified to become a near-certainty that the sun will always rise.

Thus, new evidence reshapes your opinion and consequently your actions.

SpamAssassin successfully employed the theorem above to distinguish features that characterize spam from those that characterize non-spam in messages that you receive. This software thus has the capability to learn your email environment and adapt its detection behavior to elevate accuracy on your behalf.

Microsoft even used a similar approach when developing the Microsoft Assistant, designed to be a virtual help assistant in office products.

?When a user calls up the assistant, Bayesian methods are used to analyze recent actions in order to try to work out what the user is attempting to do, with this calculation constantly being modified in the light of new actions,? said the Economist.

The article stated that future products would try to determine users’ intentions more broadly to speed things up.

?Having worked out which link on a web article a user is most likely to click on, for example, the computer could fetch the corresponding article in advance, so that it appears more quickly.?

So the next time you check your Junk folder, remember what mathematical wonders are being used to help keep your inbox clean and your computer (and Smartphone) safe!

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