**Independent-Sample t Test
{From the Institute of Phonetic Sciences (IFA):
http://www.fon.hum.uva.nl/}**

This is the standard test for two samples. It is also the
yard-stick for calculating the relative efficiency of other tests. The Student-*t*
test is the most sensitive test for interval data, but it also requires the most
stringent assumptions.

* H _{0}: *Both populations have identical mean
values. That is, the difference between the means is

*Assumptions:*

Both distributions are Normal distributed with *identical
variances*. If there is any reason to doubt these assumptions, use another,
distribution-free, test (e.g. the
Wilcoxon Test).

*Scale:*

Interval

*Procedure:*

Calculate the Mean values (*M _{1}*,

*SDg* = sqrt{[(*n _{1}*-1)*

The test statistic is

*t* = ( *M _{1}* -

The number of *Degrees of Freedom* (df) = *n _{1}
*+

*Level of Significance:*

The significance levels of *t* for different *df*
are tabulated in many introductory statistics books.

*Approximation:*

When *df* > 30, the distribution of *t* can be
approximated by a standard score,* z*, and compared to probabilities found
in the
Standard Normal Distribution.

You can also compute the *t* test by clicking here:
Independent-sample *t* test.