Category: Statistics


Lightning Strikes Way Too Much

(Submitted by reader Chad Simonds)

This is not a story about something that happened to me, nor a third person account; but I think it’s a worthy topic nonetheless.

I’m a runner who lives in Florida.  During the summer months it is just too hot and humid to go running when the sun is out, so I’ve taken to running only during thunderstorms. I understand that the odds of being struck by lightning are very minute, but I’m wondering how those odds are actually calculated.

Does the currently understood odds of being struck by lightning take into account how much time one spends outside during a thunderstorm (which is presumably less time than when it’s not raining)?  If I am effectively seeking out thunderstorms, are the odds of being struck by lightning significantly greater, or are the odds still so low that I’m not really in any danger?

[Editor: Although this is a great question for The Odds Must Be Crazy, my immediate thought was about the film The Curious Case of Benjamin Button, and the short clips of the roomer in the boarding house who was struck by lightning seven times. The odds turn out to be not so crazy!

Also - evidently being struck by lightning is not to be taken - lightly. It is the second leading weather related cause of death, after floods. According to one source, 400 people are struck by lightning in the US annually, and sixty lose their lives.

Florida is the number one state, leading the deaths by lightning at 126 from 1990-2003. If a thunder storm starts when you are out running - get inside a car or building, stay away from tall conductive objects, or curl up in a ball, making yourself as small a target as possible. -  Wendy]

Knot That Strange

Last month an article on one of my favorite websites, io9.com, grabbed my attention. It included a discussion of studies and simulations which demonstrate (and provide evidence for) some of those things in life that lead us all to think that fate is trying to tell us something. Specifically, the adage we call “Murphy’s Law” states that what can go wrong will go wrong and it is supported by both mathematical proofs and observations.

“When it comes to long strands of string, from proteins in a person’s cells to the rigging in a ship, this means spontaneous knotting. People have written papers about how string knots up the minute it’s given a chance to jiggle around.”

The article goes on to discuss a simulation of a random walk (direction for each step is determined randomly) in 3-dimensional space with the restriction that no space can be occupied more than once. The path of the walk simulates the placement of a length of string – the beginning and end of the path are the ends of the string and no part of the string can occupy the same space as another part. What the researchers found was that any sufficiently long walk (string) must contain a knot. The longer the walk (string), the more knots.

This can teach us that tossing our Christmas lights into a box is almost certain to result in knots to untangle next year, but it can also teach us a lot about risks, coincidences, and how to think about those things.

Barbara Drescher

When I was nine years old my family lived on the Great Lakes Naval Station (on the shores of Lake Michigan) for about a year before buying a house off the base. Our home was in a cul de sac that was shared by several families. One of the families of which we were particularly fond was a widower with a boy and girl about the same ages as my brother and I. Fast forward to more than four years later, after we had moved twice and now lived 2,000 miles away in Sacramento, California. We drove the three hours from our home to a tiny fishing hole called Blue Lake for a weekend of camping and fishing. About an hour after we arrived, my mother suddenly blurted out, “Hey, isn’t that Bud Neighbor [not his real name]?” Sure enough, camped a few spaces down were our old friends.

I have had quite a few similar experiences, but none as bizarre or unexplainable as this one. Should we have been freaked out and considered some cosmic connection?

To find out, let’s turn back to the article I mentioned and Murphy’s Law. Is it true that anything that can go wrong will go wrong? Well, not exactly. You can get on that plane tomorrow and be confident that you will survive the flight (your odds are approximately 9.2 million to 1). However, if you “tempt fate” enough, even the least likely disaster will eventually happen. Of course, your plan to commit suicide via commercial airliner will require you to fly every day for more than 25,000 days to ensure success, and even then you have no guarantees.

The problem of spontaneous knotting is simply a matter of odds. It relies on something called “The Law of Large Numbers”, which dictates that any event which can occur will occur if given enough opportunities.* String knots up when there’s a lot of it because there are a number of ways in which it can be knotted.

Without going through a bunch of math, let’s look at how we determine probabilities. There are two properties to consider when determining whether an event is unusual (vs. expected):

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