Contrary to Popular Belief, the Groundhog is Right More Often than Not

So there I was, thinking about Groundhog's Day.  Thinking about that prognosticating rodent.  Thinking about how he's usually wrong.  At best, he gets his predictions right about 40% of the time.  If you were randomly flipping a coin, it would come out better than that.  But the Groundhog doesn't.  And the reason why is because the Groundhog's predictions are not random.  The Groundhog doesn't have it wrong.  We do. 

 

If we are going to check the accuracy of the Groundhog (or anything, as far as that goes), we first need to quantify the information that we are trying to measure.  We must convert it to numbers.  Obviously, no matter what the Groundhog says, we're still going to have wintery days and spring-like days for the next six weeks.  There will be days that are cloudy and cool, and days that are sunny and warm.  We can measure that.  We can count how many days there are of each.  If there are more warm, sunny days than cloudy, colder days, then we can say that spring came early.  If there are more cloudy, colder days, then it didn't. 

 

Let's use the World Series as an example.  The team that wins the first game in the best out of seven series goes on to win the entire series almost 2 out of 3 times (63.7%).  Sure, teams do come back and win it all, but winning that first game switches the odds in favour of the winning team.  Whereas the other team now must win 4 of the next 6 games (67%), the team with the first victory only has to win three of the next 6 games (50%).  Because there is a finite amount of games, the odds of winning the most games shifts dramatically in favour of the team winning that first game.

 

It's the same principle with Groundhog's Day.  There is also a finite amount of days between Groundhog's Day and the "official" first day of Spring.  If the Groundhog gets the first day right, then it shifts the odds of his prediction being correct for all of those days.  But that's not how we do it. 

 

How we've always done it is if the Groundhog sees his shadow – if it's sunny on Groundhog's Day – then there will be six more weeks of winter.  Nice weather today means bad weather for the next 42 or so days.  On the other hand, bad weather today means good weather for the next six weeks.  And that's just nuts.  There's a reason why it makes no sense.  It's like a team in the World Series losing the first game on purpose.  No wonder the Groundhog is usually wrong.

 

But if we flip it, then the Groundhog suddenly becomes right 60% of the time.  And that's better than any weatherman.  Way better.  Whatever the weather is on Groundhog's Day is what the next six weeks will more than likely be, if for no other reason than we already know what the weather will be like on one of those 42 or so days, and that changes the percentage in the Groundhog's favour.  It's that simple.