Q: If some events are so unlikely to happen, why do people bet on them?Ī: A lot depends on the sort of return that is being offered. It can still be useful to double-check your results, though. Q: So I don’t have to work out probabilities by counting everything?Ī: Often you won’t have to, but it all depends on your situation. On the other hand, if you knew P(Black) and P(Red) but didn’t know how many different colors there were, you’d have to calculate the probability by adding together P(Black) and P(Red). In this situation, you’d have to calculate the probability by working out the probability of not getting a green: Suppose the only information you had about the roulette wheel was the probability of getting a green. Which way is best?Ī: It all depends on your particular situation and what information you are given. Q: It looks like there are three ways of dealing with this sort of probability. The two events are mutually exclusive, so no elements are shared between them. Similarly, if an element is in A I, then it can’t be in A. If an element is in A, then it can’t possibly be in A I. Q: Can anything be in both events A and A I?Ī: No. You’ll see more situations where this helps you later on. But sometimes they can be a useful tool for visualizing what’s going on with probabilities. Q: Do I always have to draw a Venn diagram? I noticed you didn’t in that last exercise.Ī: No, you don’t have to. You don’t have to already know any set theory to use Venn diagrams to calculate probability, though, as we’ll cover everything you need to know in this chapter. In set theory, the possibility space is equivalent to the set of all possible outcomes, and a possible event forms a subset of this.
Is there a connection?Ī: There certainly is. Q: I’ve seen Venn diagrams before in set theory. As long as the probability is expressed in some form as a value between 0 and 1, it doesn’t really matter. Q: Are probabilities written as fractions, decimals, or percentages?Ī: They can be written as any of these. It can help you make sense of apparent randomness. Probability theory can help you make predictions about your data and see patterns. A lot of statistics has its origins in probability theory, so knowing probability will take your statistics skills to the next level. Q: Why do I need to know about probability? I thought I was learning about statistics.Ī: There’s quite a close relationship between probability and statistics. Here are some examples on a probability scale. A lot of the time, you’ll be dealing with probabilities somewhere in between. If it’s an absolute certainty, then the probability is 1. If an event is impossible, it has a probability of 0. Probability is measured on a scale of 0 to 1. In stats-speak, an event is any occurrence that has a probability attached to it-in other words, an event is any outcome where you can say how likely it is to occur.
You can use it to indicate how likely an occurrence is (the probability that you’ll go to sleep some time this week), or how unlikely (the probability that a coyote will try to hit you with an anvil while you’re walking through the desert). Probability is a way of measuring the chance of something happening. Have you ever been in a situation where you’ve wondered “Now, what were the chances of that happening?” Perhaps a friend has phoned you at the exact moment you’ve been thinking about them, or maybe you’ve won some sort of raffle or lottery.
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