## Introduction to Hypothesis Tests

Hypothesis testing is a common method of drawing inferences
about a population based on statistical evidence from a sample.

As an example, suppose someone says that at a certain time in
the state of Massachusetts the average price of a gallon of regular
unleaded gas was $1.15. How could you determine the truth of the statement?
You could try to find prices at every gas station in the state at
the time. That approach would be definitive, but it could be time-consuming,
costly, or even impossible.

A simpler approach would be to find prices at a small number
of randomly selected gas stations around the state, and then compute
the sample average.

Sample averages differ from one another due to chance variability
in the selection process. Suppose your sample average comes out to
be $1.18. Is the $0.03 difference an artifact of random sampling or
significant evidence that the average price of a gallon of gas was
in fact greater than $1.15? Hypothesis testing is a statistical method
for making such decisions.