Descriptive statistics

Collection, organization, and analysis of data.

Inferential statistics

Making generalizations or predictions from the data collected.

Population

All of the items of interest.

Sample

A subset of all the items of interest.

Unbiased sample

A small replica of a subset of all the items of interest.

Random sampling

List all of the employees in a company, and give each employee a unique number.  Then devise a method for selecting 30 employees in no particular order to interview for an employee satisfaction survey.

Systematic sampling

Pull every 10th product off of the assembly line, and examine it for defects.  Multiply the number of defects counted by 10 to discover the projected total number of defects during the day.

Cluster sampling

In an order of 25,000 nails, packed in 250 boxes, select 10 boxes, count the number of defective nails, and multiply that  by 25 to determine the total number of defective nails in one the order.

Stratified sampling

Discover the buying preferences of first-year college women by interviewing 30 first-year women.

Convenience sampling

Go to the election poll, and interview the first ten people who come out of the polling station to determine the percentages of votes received by the candidates in the election.

Mean of a sample

x-bar

Mean of a population

μ (mu)

Standard deviation of a sample

s (sigma of a sample)

Standard deviation of a population

σ (sigma)