In many situations, a general form for a 
% confidence
interval for a parameter 
is
[
^ (critical value)SE(^ ),
]
where 
is a sample
statistic used to estimate , SE 
[the standard error of ] gives the variation
of and the critical value is a
value such as 
or 
.
Thus, all we have to do is (1) find
the formula for SE and (2)
``plug-in'' numbers into this general equation to get a confidence
interval. The following confidence (prediction) intervals all follow this rule.