Parameters & Statistics (College Board AP® Statistics): Revision Note

Parameters & statistics

What are parameters?

• A population refers to the whole set of things that you are interested in

  • For example, if a vet wanted to know how long a typical French bulldog slept for in a day, then the population would be the sleeping times of all the French bulldogs in the world

• A population parameter is a numerical value that describes a characteristic of the population

  • For example, if the population is all the heights of 16-year-olds in the US

    • then the mean height of all 16-year-olds in the US is a population parameter

• Population parameters are usually unknown

What are statistics?

• A sample statistic (often just called a statistic) is a value computed using data from a sample taken from the population

  • For example, the mean height of 200 16-year-olds from randomly selected cities in the US is a sample statistic

• Sample statistics are frequently used to estimate population parameters

What notation is used to represent parameters and statistics?

• The notation used for a particular variable can often indicate if it is a population parameter or a sample statistic

  • Greek letters are used for population parameters

  • English letters are used for sample statistics

• The sample mean,

  • is used to estimate the population mean,

• The sample standard deviation,

  • is used to estimate the population standard deviation,

• There is only one exception to the rule in this course:

  • the sample proportion, , is used to estimate the population proportion,