Harmonic mean is an alternate form of average that focuses on the mid-range numbers of a given set. It can be a powerful tool in calculations that involve the comparison of extremely different values. Whereas the traditional mean of a set of numbers equals the sum of those numbers divided by their quantity, the harmonic mean uses the reciprocal number of the set and figures in the sum of its reciprocals. While it is a relatively simple process to determine the harmonic mean, it can be applied to a number of information-comparison scenarios.
The harmonic mean value of a set can help account for the outlier numbers that skew the standard mean. Imagine a set containing the numbers from 1 to 10. The traditional mean of the set is 5.5, but if the set consisting of numbers 1, 6 and 10, the harmonic mean is (1/1 + 1/6 + 1/10 = 5.9), which isolates the midpoint of the set and eliminates the higher and lower values. This is beneficial when dealing with populations with a large discrepancy among individuals. For example, if a group of 7 employees have salaries of $20,000, $30,000, $60,000, $70,000, $75,000, $90,000 and $100,000, the traditional mean salary is $64,285.71, which gives the impression that the majority of employees are making close to the average. The harmonic mean, however, comes to $55,555.55, which more accurately reflects the extreme number of employees on the lower and upper ends of the range.
Another practical application of harmonic mean involves calculating the speed of a driver traveling at different speeds over a set period of time. If a driver travels 10 miles in 10 minutes, 10 miles in 20 minutes, 10 miles in 30 minutes and 10 miles in 40 minutes, the traditional mean comes to 25 mph, which reflects the total miles over total minutes. The harmonic mean, however, comes to 17.64 mph, which takes into consideration that two thirds of the time was spent going slower than 25 mph.
Harmonic mean can also be used in population measurement. If a certain fish population consists of 7 fish that weigh 200, 500, 1,300, 2,000, 2,500, 3,000 and 3,500, the traditional mean weight is 2,471 and indicates that the majority of fish in the population weigh about 2,400 grams. However, the harmonic mean of 980 gives more insight into the fact that the majority of the population is nearer to the lower end of the range.
Harmonic mean can be a useful tool in many applications. It offers a different perspective on the midpoint of a set and can bring to light dramatic discrepancies that are often unleashed by the traditional mean.