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Tag: gambler’s fallacy

Hurricane Sandy and the gambler's fallacy

There are presently no shortage of articles being written about Hurricane (now Post-Tropical Cyclone) Sandy and what role climate change has played in the formation of the "Frankenstorm" that has left over 7.5 million people without power. I came across one article, however, that should be addressed: Hurricane Sandy: The Worst-Case Scenario For New York City Is Unimaginable (by Mike Tidwell, at

Much of the article is a traditional "worst-case scenario" description found commonly in the media for seemingly all combinations of disasters and major cities. Of note, however, is the following paragraph (emphasis added):

Another major storm struck in 1892, then another in 1938 when the borderline Category 4 “Long Island Express” passed through the outskirts of greater New York, inflicting widespread death and destruction across New York state, New Jersey and much of New England. But that storm, 68 years ago, was the last major hurricane (Category 3 or above) to strike the New York Metropolitan region. It’s now a matter of when, not if, a big hurricane will strike again, according to meteorologists. And history says “when” is very soon.

The bolded statement is a classic example of the gambler's fallacy. It seems as if hurricanes can be reasonably modeled by a Poisson process, a useful probability model (e.g. this website, this paper (pdf), and this paper (pdf)), and this assumption will be used throughout this post.

One of the important properties associated with this model is called memorylessness. Essentially, what this means is that at any given time period, the probability of an event occurring does not depend on the history up to that point. That is, it doesn't matter how long a system has been running, a 'success' is just as likely to occur at this time period if this is the first time period, if this is the 10th time period, or if this is the 76th time period.

For example, when playing roulette, the probability of spinning a 'black' are the same on every spin, irrespective of how many times you have previously spun the wheel. Even if there have been 999 'red' in a row, we are not 'due' for a black spin (assuming the wheel is fair, etc.).

Just because New York City hasn't had a major hurricane for a while does not mean that it is due or overdue for one. Each hurricane season is a new cycle and does not remember the previous years' hurricanes.

I am not an expert in the fields of research associated with most disasters, but this makes sense in terms of hurricanes (both from various sources and my life as a Floridian). For other disasters (e.g. volcanoes and earthquakes), my understanding is that pressure builds over time and therefore reasonable models for those systems should not have the memorylessness property, so perhaps talking about 'overdue' for a major disaster is warranted. Maybe not, but I do want to emphasize that this is specific to hurricanes.

(It might also be worth checking out these comics related to the gambler's fallacy.)

Satellite image of Hurricane Sandy (25 October 2012)
Satellite image of Hurricane Sandy (25 October 2012)
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Another Gambler's Fallacy comic

Another fine statistics comic related to the Gambler's Fallacy comes from Tree Lobsters, a comic that I didn't expect to keep reading... and yet I did. The site's comics are mostly a mixture of science in public policy and general nerd humor, and there is a good search feature to help identify relevant comics.

Wow! I've flipped five heads in a row. This next one's gotta be tails, then. Doesn't work like that. The previous results don't affect the probability of future events. The chances of flipping six heads in a row are 1 in 64 but the chances of flipping heads after 5 in a row are still 50:50. While you were busy lecturing, I flipped another 20 heads in a row. What's your logic say to that? Vegas road trip? I'll start packing.

The chances of 25 heads in a row are 1 in 33 million, which is still 6 times as likely as winning the Powerball jackpot. So, you've got to ask yourself one question: 'Do I feel lucky?'
"#76 Dumb Luck" - Copyright 2008-2012, Tree Lobsters
keywords: gambling; Gambler's Fallacy; coin; coin flip; probability; luck;

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Dinosaur Comics!

While looking for more probability and statistics comics, I went to one of my favorite webcomics: Dinosaur Comics. A handy resource for finding individual Dinosaur Comics is this XML file which contains all the text of every comic (I think). Ctrl+F is the way to go for finding comics of interest. While there are numerous comics that mention statistics, the relationship is usually tangential at best.

you can show this comic to chronic gamblers and they will PUNCH YOU IN THE NECK
"gambling makes you appear more attractive in the eyes of women" - Copyright 2004 by Ryan North, Dinosaur Comics
keywords: probability; Gambler's Fallacy; dice; luck;

On an unrelated note, Dinosaur Comics has one of the best alternate URLs in existence: Food for thought.

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