Why randomness doesn’t always look random

I got the lightning puzzle that I posed yesterday from the latest book by Steven Pinker The Better Angels of Our Nature: Why Violence Has Declined that I reviewed in December. He uses it to illustrate that our intuitive notions of randomness and probability can easily lead us astray.

Here is the problem again.

Suppose you live in a place that has a constant chance of being struck by lightning at any time throughout the year. Suppose that the strikes are random: every day the chance of a strike is the same, and the rate works out to one strike a month. Your house is hit by lightning today, Monday. What is the most likely day for the next bolt to strike your house?

Here is his answer followed by [Read more…]

When is lightning most likely to strike again?

Since I have been taking about probabilities recently, here is a little puzzle for people to ponder overnight.

Suppose you live in a place that has a constant chance of being struck by lightning at any time through the year. Suppose that the strikes are random: every day the chance of a strike is the same, and the rate works out to one strike a month. Your house is hit by lightning today, Monday. What is the most likely day for the next bolt to strike your house?

Feel free to post your answers in the comments. I will give the answer tomorrow along with a discussion.

Blogs with homework. Now there’s a novel concept!

Update: The solution and discussion are posted here.

Probabilities and false positives

In response to my post on random drug testing in Florida, commenter Scott mentioned the danger of false positives and said that a second test in his case cleared him of having taken drugs. My advice to anyone is that whenever you take a high-stakes test for anything that has a small incidence in the general population (drugs, diseases, whatever) and it comes out positive, always consider asking for a second test.

Here’s why. [Read more…]

An old Earth, population bottlenecks, and Adam and Eve

It is always interesting to see religious people trying to find ways to reconcile modern science with their religious texts. For people who have a literal interpretation of the Bible, the task is much harder, with the Genesis story being a nightmare. This is not because the Genesis story is particularly crazier than the other miraculous stories in the Bible but because it is the most familiar and you cannot easily finesse it away. Everyone knows the general outlines of it, even if they are [Read more…]

Using drug tests to humiliate people

Aasif Mandvi from The Daily Show goes to Florida to investigate their policy of forcing people to take drug tests in order to get welfare benefits. It is quite extraordinary the lengths these people will go to make people who are down on their luck feel like scum.

To get suggestions on how to view clips on The Daily Show and The Colbert Report outside the US, please see this earlier post. This clip appeared on February 2, 2012.

How rich people can pay little or no taxes

Most of us think that people who have made a ton of money by various means then simply invest it and live off the resulting income. But what form does this investment income take? If you are an average person, you tend to think of investment income as the interest on certificates of deposit or savings and money market accounts, which are taxed at the same rate as ordinary income. More sophisticated investors get their investment income in the form of [Read more…]

Atheists seek recognition in the US military

Sgt. Justin Griffith is trying to get the US Army to provide to atheists the same kinds of support and services that they provide to religious groups. He is organizing on March 31, 2012 Rock Beyond Belief, that is advertised as “a day-long event on the military base Fort Bragg, North Carolina, complete with children’s activities, rock concerts and [Read more…]