C9 Probability and Probability Distributions

• The ability to make statistical inferences is based on knowledge of the probability distribution appropriate to the situation.
• theoretical probability is known from a mathematical model, called the binomial expansion, which is appropriate for dichotomous (two-value) variables, such as heads/tails, correct/incorrect, or present/absent.
• If all possible outcomes are equally likely, the probability of the occurrence of an event is equal to the proportion of the possible outcomes favoring the event.
• You must use the t-distribution table when working problems when the population standard deviation (σ) is not known and the sample size is small (n<30). General Correct Rule: If σ is not known, then using t-distribution is correct.