
Biological
significance 
"Biological significance" (as contrasted
with statistical significance)
refers to a statistically significant effect that has a noteworthy
impact on health or survival. If an observed effect is small
but quite precise (i.e., there is little uncertainty in the
observed value), the effect can be statistically significant
even if it isn't biologically significant. For example, a
factor that causes a decrease in blood pressure of 1 mmHg
on the average can be statistically significant if tested
in a large group of people, but an average reduction of 1
mmHg in blood pressure has no practical clinical implication
per se. 

