Statistics for CSAI 2

by Albert Major

Probability recap

Probability underpins inferential statistics.

Key ideas

• Elementary event: one specific outcome.
• Sample space: all possible outcomes.
• Sum of all probabilities equals 1.
• Non-elementary event = combination of outcomes.

Why probability matters

• You study a sample, not a whole population.
• Probability tells you how likely your sample observations are.
• All inferential tests compute some probability of seeing your data if a null hypothesis is true.

Binomial distribution

Used for success vs non-success outcomes. (two possible outcomes)

Examples:

• Rolling a special die with one “skull” out of 6 sides.
• Probability of getting a certain number of skulls in 20 rolls.
• Pizza example: vegetarian vs meat pizza.