Mathematics and Applied Statistics Lesson of the Day – The Weighted Harmonic Mean

June 25, 2014 5 Comments

In a previous Statistics Lesson of the Day on the harmonic mean, I used an example of a car travelling at 2 different speeds – 60 km/hr and 40 km/hr.  In that example, the car travelled 120 km at both speeds, so the 2 speeds had equal weight in calculating the harmonic mean of the speeds.

What if the cars travelled different distances at those speeds?  In that case, we can modify the calculation to allow the weight of each datum to be different.  This results in the weighted harmonic mean, which has the formula

H = \sum_{i = 1}^{n} w_i \ \ \div \ \ \sum_{i = 1}^{n}(w_i \ \div \ x_i).

 

For example, consider a car travelling for 240 kilometres at 2 different speeds and for 2 different distances:

  1. 60 km/hr for 100 km
  2. 40 km/hr for another 140 km

Then the weighted harmonic mean of the speeds (i.e. the average speed of the whole trip) is

(100 \text{ km} \ + \ 140 \text{ km}) \ \div \ [(100 \text{ km} \ \div \ 60 \text{ km/hr}) \ + \ (140 \text{ km} \ \div \ 40 \text{ km/hr})]

= 46.45 \text{ km/hr}

 

Notice that this is exactly the same calculation that we would use if we wanted to calculate the average speed of the whole trip by the formula from kinematics:

\text{Average Speed} = \Delta \text{Distance} \div \Delta \text{Time}

Filed under Applied Statistics, Mathematics, Statistics, Statistics Lesson of the Day Tagged with , , , , , ,

5 Responses to Mathematics and Applied Statistics Lesson of the Day – The Weighted Harmonic Mean

  1. Matthew Dorey says:
    June 27, 2014 at 1:32 pm

    Nice post. Will be following from now on.

    Reply
  2. ibrahim balele says:
    February 21, 2016 at 12:00 am

    Ibrahim Balele from Tanzania. I do appreciate your efforts for providing us studying materials,God bless you!

    Reply
  3. dlidstrom says:
    March 19, 2020 at 4:43 am

    So the weighted harmonic mean is actually the arithmetic mean of the whole? Interesting!

    Reply

Your thoughtful comments are much appreciated!