Just before Christmas, Shirley and I completed a series of **Teaching Company** lectures on probability by Michael Starbird, Professor of Mathematics at the University of Texas at Austin. A course like this is a must for anyone who 1) lacks formal training in mathematics and 2) lives in this world. Probability is involved of almost ever decision we make and nearly everything that happens to us and to the world around us. When we talk of weighing the evidence, we really mean that we are accessing the extent that a certain set of evidence increases or decreases the probability of something or other being the case.

If you take the link to the course, don’t panic at the price. The Teaching Company wildly discounts these prices on a regular basis. I think we paid about $40.00 rather than the nearly $200.00 list price. I can’t quite figure out their pricing strategy. I guess they want you to keep coming back to see what’s on sale. Also, don’t panic if you have math phobia or don’t think that you are good at math. This is a math course that requires nothing more than arithmetic and not much of that. It is largely build around easy to understand examples that illustrate the underlying concepts. Physics, biology, finance, meteorology, tactics in sports all come into play. Starbird’s discussion of what meteorologists mean by a “30% change of rain” not only answered the question but also pointed the way to a host of abnormally interesting issues. I was particularly happy to see that Starbird dedicated two lectures to Bayesian probability and the larger question of how we learn and make decisions from incomplete data. While long ago I studied probability in a formal setting, I found this course was both fun and helpful. I highly recommend it.

## 4 thoughts on “What Are The Chances?”

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About a month ago I bought part 1 of Great Ancient Civilizations of Asia Minor by Kenneth Harl from the used bookstore for $10. Since I don’t have time to listen to such things at home, I am going to transfer the lectures to my iPod & then listen to them during my daily walks. Let’s see if I can walk & learn at the same time.

Since we have nothing but time we enjoy watching the DVDs. Most (all?) of the math and science courses are only available on DVD and would be very hard to follow them without the video.

So what exactly does “30% chance of rain” mean?

Is it that there is a 30% chance that rain will fall on at least one spot in the area at some time during the day?

Or 30% of the area will get some rain?

Or at any time,30% of the area will be experiencing rain?

I’ve always felt that the weather people didn’t want to produce a specific definition.

According to Starbird, “The probability of precipitations (PoP) is defined as the likelihood (expressed as a percent) of a measurable amount (0.01 inch or more) of liquid precipitation (or the water equivalent of frozen precipitation) during a specified period of time

at a random pointin the forecast area.” This is slightly different but mathematically more correct than the definition provided by the National Weather Service. The Weather service reads “at any given point” where Starbird’s definition reads “at a random point.” He thinks the Weather Service tried to make the definition more understandable to the layperson and in so doing actually gives a somewhat misleading answer. The 0.01 inch level is by definition.