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 Monday, November 06, 2000 #3945

How and when do you do a weight average?
 The Media Guru Answers(Tuesday, November 07, 2000 ):

weighted averages are used to calculate the overall average when you have percentages of various groups that are parts of the larger whole. Click here to see past Guru
responses using weighted averages.
 Monday, June 12, 2000 #3547

I am buying radio in two different markets  one is a large market which is measured by Arbitron. The other is a small market where I get the ratings through Arbitron county measuring.
The two cities are only 45 miles apart and there is a large amount of radio overlap. Is there any way to figure an accurate combined reach & frequency? Thanks.
 The Media Guru Answers(Monday, June 12, 2000 ):

First, define "market." If these radio markets are both in the same DMA, and you want DMA R&F, add the two stations' reach in thousands and divide by DMA universe. If they are in two different Metros, calculate reach within each and do a weighted average of the two:
 Metro "A" target population = 100,000
 Metro "B" target population = 20,000
 Metro "A" target reach = 40% (40,000)
 Metro "B" target reach = 55% (11,000)
 Combined, total coverage area reach = 40,000 + 11,000 ÷ 100,000 + 20,000, or 42.5%
 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 1824 and 3.0 for Adults 2549, so what is the 1249 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, A1824 is 24.7 million and A2549 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.
 Tuesday, October 08, 1996 #1133

I wonder if you could enlighten me on your thoughts onthe following: currently, within our market, we lookat cost per point (CPP) for TV. This has been the casefor a number of years now. Recently, however, certainTV stations have been trying to encourage the use ofcost per thousand (CPT). Is there any right or wrongway of looking at a cost measurement for TV?My thinking is that CPT does not prove to be stablewhen measured across a time period, simply becauseuniverse sizes change over time (thousands do increasebut not necessariily the penetration into a market).Therefore CPT could be used when measuring off the sameuniverse size, but is not feasible in showing trendsover different years using different universe sizes.CPT works to the advantage of the media owners as it isseen as much less of an amount than a CPP is (at themoment)???Please help.
 The Media Guru Answers(Wednesday, October 09, 1996 ):

The issues you raise with the use of CPT as against CPP are real, particularly in that when you have people meter data and the universes are changing they will affect the 'thousands' calculated conceivably more than the change in the audience itself.
In people meter panels the universe can vary if it does not form part of the weighting cells. In addition as a rating using people meter data is a time weighted average it is not strictly speaking possible to convert them into whole 'people'. Selling or buying TV based on CPT derived from respondent level people meter data would be fraught with hidden difficulties for both the users and the TV stations. Note that this question was posed about the South African market.
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