Probability Fundamentals Vocabulary

a measure of the likelihood that an event will occur

“The probability of rolling a six is 1/6.”

Origin: Latin probabilitas `credibility`, from probare `to prove, test`

randomly determined; having a random probability distribution

“Stock prices follow a stochastic process.”

Origin: Greek stokhastikos `able to guess`, from stokhos `aim, guess`

a variable whose value is determined by chance

“The number of heads in 10 coin flips is a random variable.”

Origin: From random (Old French randon `rush, disorder`) + variable

the long-run average value of a random variable

“The expected value of a fair die roll is 3.5.”

Origin: From expect (Latin exspectare `to look out for`) + value

a measure of how spread out a distribution is

“High variance indicates data points are far from the mean.”

Origin: Latin variantia, from variare `to change`

the square root of variance; a measure of dispersion

“Most data falls within two standard deviations of the mean.”

Origin: From standard + Latin deviare `to turn aside`

a function showing all possible values and their probabilities

“Test scores often follow a normal distribution.”

Origin: Latin distributio `division`, from distribuere `to distribute`

events where one does not affect the probability of another

“Successive coin flips are independent events.”

Origin: Latin in- `not` + dependere `to hang from`

the probability of an event given that another has occurred

“The conditional probability of rain given clouds is higher than without.”

Origin: From condition (Latin condicio `agreement`) + probability

a formula for updating probabilities based on new evidence

“Bayes' theorem helps doctors interpret diagnostic test results.”

Origin: Named after Thomas Bayes, English statistician (1701-1761)