Statistics · Statistical distributions
Chapter 1 · 3
The idea
Discrete random variables and probability distributions
What a discrete random variable is, and how a probability distribution lists each value it can take with the probability of that value — as a table or as a probability function. The key rule that the probabilities must sum to 1 (used to find an unknown), reading cumulative probabilities like P(X ≤ 2) off a distribution, and the special case of a discrete uniform distribution.
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Statistics · Statistical distributions
Discrete random variables and probability distributions
What a discrete random variable is, and how a probability distribution lists each value it can take with the probability of that value — as a table or as a probability function. The key rule that the probabilities must sum to 1 (used to find an unknown), reading cumulative probabilities like P(X ≤ 2) off a distribution, and the special case of a discrete uniform distribution.
Why it works
A quantity decided by chance
Until now, probability has been about events — "rolling a six", "picking a red". This chapter promotes the number itself to the random object. A random variable is a quantity whose value is decided by chance — the score on a die, the number of heads in three tosses. We write random variables with capital letters (, ) and the particular values they take with small letters (). A discrete random variable can only take separate, listable values (usually whole-number counts).Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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