Analysis of Variance (ANOVA)
is a statistical technique that is used
to compare whether samples are drawn from
populations that have the same mean
(average), or whether the population means
are significantly different. For example
a manufacturer might have five potential
suppliers of a steel for an application
where strength is important and want to
know if the average strength of the steel
from all five suppliers is essentially the
same.
The ANOVA method analyses the variation
in the data set to discover the amount of
variation that can be attributed to each
factor. In the example there is only one
factor, the strength of the steel. The ANOVA
method also calculates the amount of ‘common
cause variation'.
A hypothesis
test is then carried out to
see if the amount of variation from each
source is statistically significant. The
test uses the F Test
to compare the variation due to each factor
to the amount of 'common cause variation'
See One
Way ANOVA and Two
Way ANOVA for worked examples.
The ANOVA method requires the process conforms
to a normal distribution. Refer to Nonparametric
Tests for nonparametric equivalents.
