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Media Guru

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Wednesday, July 28, 1999 #2666
How are weighted averages calculated?

The Media Guru Answers(Saturday, July 31, 1999 ):
Each value in a series is multiplied by its appropriate weight and the sum of the products is divided by the sum of the weights. Example:
  • The ratings of a TV program are 5.0 for teens, 4.0 for Adults 18-24 and 3.0 for Adults 25-49, so what is the 12-49 rating?
  • It's not the straight average of 5.0, 4.0 and 3.0, or 4.0; we must account for the different sizes of the populations in these three age groups.
  • Let's suppose the teen population is 22.5 million, A18-24 is 24.7 million and A25-49 is 103.3 million. We multiply each rating by its population base:
    5.0 x 22.5 = 112.5
    4.0 x 24.7 = 98.8 and
    3.0 x 103.3 = 309.9
  • Sum the products: 112.5 + 98.8 + 309.9 = 521.2
  • Sum the weights:
    22.5 + 24.7 + 103.3 = 150.5
  • Divide the sum of products by the sum of weights
    521.2 103.3 = 3.5 correct (weighted) average rating.



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