“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.