Statistical Glossary
Harmonic Mean:
Harmonic mean is a measure of central location. The harmonic mean 
of 
positive values 
is defined by the formula
 |
Let the path between two cities 
and 
be divided into 
parts of equal length. One drives the 
th part at velocity 
. Then, the average speed on the whole journey is the harmonic mean 
of velocities 
.
The harmonic mean is sensitive to a single small value - 
tends to be small if at least one of the values 
is abnormally small. (In the above example, this corresponds to very slow driving through one of the road parts, leading you to spend most of the journey on this part of the path).
For this reason, the harmonic mean is often used, for example, to aggregate scores in different types of activity to a single final score, e.g. to estimate students´ performance. This ensure that no partial scores are radically lower than the final score.
See also Mean values (comparison) .