
Statistical
significance 
"Statistical significance" (as contrasted
with biological significance) means statistical analysis has revealed an effect unlikely to have occurred
by chance alone. The level of significance refers to the degree to which
the result could be explained by chance. At the 0.05 (5%) level the result
could have occurred by chance 1 time in 20; at the 0.01 (1%) level the
result could have occurred by chance only 1 time in 100. Any effect observed
in a study or experiment carries with it some degree of uncertainty, or
imprecision, because of randomness and variability in most biological phenomena.
Statistical techniques evaluate an observed effect in view of its precision
to determine with what probability it might have arisen by chance (the
level of significance). Values with a low probability of occurring by chance
are called "statistically significant" and are thought to represent
a real effect. 

