Routine application of significance tests does not extract the maximum
information from environmental data and can lead to misleading conclu
sions. Reasons leading to this are: a significant result can often be
reached merely by collecting enough samples; a statistically significa
nt result is not necessarily practically significant; and reports of t
he presence or absence of statistically significant differences for mu
ltiple tests are not comparable unless identical sample sizes are used
. These problems are demonstrated by application to pH data for grazed
and retired fields, and by discussion of significance tests used in r
ecent US regulations for groundwater quality. The advantages of equiva
lence tests, where the tester must state the difference of practical d
ifference, are discussed and applied to the field pH problem. We recom
mend that environmental managers and scientists pay more attention to
statistical power and decide on what is a practical difference. Confid
ence intervals for the size of the differences, accompanied where nece
ssary by equivalence tests, are the preferred means of addressing the
question: ''is there a difference of practical significance?''