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Even though there have been many lottery winners, the
chances of any one of us winning are hard to think about.
Credit: adrigu, used via Flickr Creative Commons licence. |
by Gaia Cantelli, PhD
What are your chances of winning the lottery? How about of making it big in Hollywood, transmitting a genetic disease to your child or dying of cancer? Some would say it’s 50:50, you either do or you don’t. But they’d be wrong.
Many decisions in life, big and small, are based on understanding probability. But how well do you really know how probability works? Taking the time to understand it could change your life.
Probability 101
We are all familiar with the idea of probability as the likelihood that any given event is going to happen. In mathematical terms, however, it is defined as the ratio of “favourable” cases, or the scenario whose probability you are measuring to the whole number of possible cases. This sounds complicated, but it’s really not. Say that you have a drawer full of pens and you know that ten of them are blue and three of them are red. You want a red pen – this is your favourable case. What’s the chance of getting a red pen?
The probability of you putting your hand in the drawer blind-folded and pick up a red pen is the number of red pens – three – divided by the overall number of pens – the three red pens plus the ten blue pens, which makes thirteen pens. Three divided by thirteen is 0.23, or 23%. So you have a 23% chance of picking up a red pen if you stick your hand in the drawer.
A simple calculation of probability is very useful for some events where everybody’s chances are the same, like buying a lottery ticket. For example, the US Lotto sells about 30 million tickets every draw. Therefore, if you only buy one ticket your probability of winning is one over 30 million, which computes at about 0.000003%. That’s much, much less than 50:50. But what does such an extreme number actually mean? Hold on, we’re getting to that.
