"Dave" wrote:

We are trying decipher whether to use one or two tails in a t-test... what do
we do.. and what do they mean???? HELP
Dave

It depends on what you are trying to prove. If you reckon that the subject
is likely to be over (or under) the average then that is your hypothesis and
you will go for a one tail test. At 95% confidence level that means that the
subject will only be less than that in 1 out of twenty times. The 5% must all
be in one tail of the Normal curve.

In a two tailed test the results can be either above or below the average.
95% confidence is split 2½% below and 2½ above.

Hope this helps

Peter atherton