### 5.3 Hypothesis Testing

One of the most fundamental purposes of statistical analysis
is hypothesis testing.
Researchers commonly need to test hypotheses about a set of data.
For example, she might want to test whether one set of data comes from
the same distribution as another,
or
whether the mean of a dataset significantly differs from a particular
value.
This section presents just some of the possible tests that PSPP offers.

The researcher starts by making a *null hypothesis*.
Often this is a hypothesis which he suspects to be false.
For example, if he suspects that `A` is greater than `B` he will
state the null hypothesis as `A` = `B`.

The *p-value* is a recurring concept in hypothesis testing.
It is the highest acceptable probability that the evidence implying a
null hypothesis is false, could have been obtained when the null
hypothesis is in fact true.
Note that this is not the same as “the probability of making an
error” nor is it the same as “the probability of rejecting a
hypothesis when it is true”.