AP Stats

Unit 1 (A - E)

Observational Unit

Something being described by a set of data (can be a person, animal, or thing).

Population

Entire group of observational units we want to learn something about.

Say “ALL _”

Sample

Subset of the population that we collect information from. n = “sample size”

Be specific!

Census

An attempt to collect information from every single individual in a population

Parameter

A number that describes some characteristic of a population

Usually unknown, so say “the true _”

Statistic

A number that describes some characteristic of a sample

(also called a
“point estimate”)

“P goes with P”

Parameters describe Populations

“S goes with S”

Statistics describe Samples

Variable

A characteristic that can take different values for different individuals

Distribution

Tells us what values the variable takes and how often it takes those values

Categorical Variable

A variable that groups individuals together into similar categories

Quantitative Variable

A variable that is a quantitative number
(makes sense to take an average)

Not all numbers are quantitative!

• Phone number

• Zip code

• Grade level

Discrete Variable

A quantitative variable that takes a fixed set of possible values
(0, 1, 2, …)

Usually a result of counting

Continuous Variable

A quantitative variable that can take any value on a number line

Usually a result of measuring

FREQUENCY

How often something occurs as a counted number

RELATIVE FREQUENCY

How often something occurs as a percentage

(often called a proportion)

P hat

Used when you are describing the true proportion (PARAMETER)

Example: p̂ =

P

Used when you are describing the true proportion (PARAMETER)

Example: p = ?

BAR GRAPH