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 Friday, June 29, 2001 #4538

Hello again,
I have two questions about calculating reach and frequency that I have been unable to find in the archives of past responses. Perhaps you can help?
1. I normally use the formula (a+b)(.a*b) to determine combined reach of two mediums, such as radio and print. How do I calculate the combined reach of more than two? The plan I am working on includes spot TV, spot radio and local newspaper.
2. Is it possible to determine a combined reach for more than one market or should each market be reported separately? In the past, I have provided separate delivery for each market in the same plan with a total number of gross impressions for the whole plan. Is this correct?
Thanks in advance!
 The Media Guru Answers(Friday, June 29, 2001 ):

1. This common formula is based on an assumption that different media duplicate their audiences according to random probability. Therefore if you follow this assumption, media may be added to combinations of media in a "chain" of the same formula. So, once you have combined TV and Radio, you can use this combination as your "a" and then combine it with newspaper as "b."
2. You can combine reaches across markets by doing a weighted average. Multiply the reach in each market by the percent of U.S. in each market. Add all the products and divide by the sum of the % U.S.
 Thursday, March 16, 2000 #3326

Dear Guru:
I would like to know if there is any equation to calculate media mix reach?
 The Media Guru Answers(Thursday, March 16, 2000 ):

There are several, equivalent ways to express the arithmetic to combines media according to random probability, which has been found generally adequate for the purpose of multimedia combination.
Here's an easy one:  Work with two reaches at a time
 Treat the reach of each medium as a decimal (50 reach is 0.5)
 Add reach of medium A and medium B
 Multiply reach of medium A by Reach of medium B
 Subtract the product of the multiplication from the sum of the addition
Example:  Reach of medium A = 40, reach of medium B = 55
 0.4 + 0.55 = 0.95
 0.40 x 0.55 = 0.22
 0.95  0.22 = 0.73
 Combined reach is 73
To add additional media, treat the combination as medium A and the next medium as B.
In some cases, a planner may have access to research which shows that an adjustment should be made for actual, measured, duplication between different media, rather than use the "random probability" formula above. In that case, more sophisticated reach calculating software packages, such as those from
Telmar allow you to make the calculation and build in known adjustments.
 Tuesday, September 14, 1999 #2792

What can you tell me about reachbased planning?
Thank you in advance.
 The Media Guru Answers(Tuesday, September 14, 1999 ):

>
The usual assumption is that print and broadcast duplicate with random probability, there is no special, greater or lesser likelihood that persons in the audience of the print schedule will also be or not be in the audience of the broadcast schedule.
Mechanically. the combination may be calculated in a few equivalent ways. The Guru finds it easiest to consider the reaches as decimals (50% reach = 0.50). Subtract the reach of print from 1 and multiply this by 1minus the reach of broadcast. Suppose print has a 40% reach and broadcast has 55%. By subtracting 0.4 from 1 (1  0.4 = 0.6), you have the probabilty of the target not being exposed to print. Subtract 0.55 from 1 to get the probability of not being exposed to broadcast (1  0.55 = 0.45)
Multiply these two together (0.6 * 0.45 = 0.27) and you have determined there is a 27% probability of people not being exposed to either of the combined media, or a 73% reach.
This formula is typically used in media software to combine different media. Certainly there are cases where there is a somewhat better than random probabilty of media duplication, such as TV Guide combining with a TV schedule, but that's the exception, calling for judgement.
 Friday, April 30, 1999 #2481

Is there any way to calculate duplication across a media plan using several media (e.g. print and radio and TV), or can I only get a duplication analysis within a media (radio duplicaton and then another duplication factor for print, etc , etc)
I use telmar for research with simmons and arbitron access and we also use JDS for buys.
 The Media Guru Answers(Friday, April 30, 1999 ):

The standard assumption in media planning is that duplication between different media is purely at random. Therefore, the random probability formula is used:
 Express the reach of each medium as a decimal (50% reach = 0.5)
 Multiply the reach of one medium by another to determine the duplication.
 Subtract the duplication from the sum of the two reaches to get the net reach
So, if you have a 40% reach in TV and a 55% reach in Print, multiply
0.4 x 0.55 to get 0.22
subtract 0.22 from 0.4+.55 and get 0.73 or 73% reach of the combined media.
There are a variety of ways to do the calculation. The Guru actually prefers to use the probablilty of not seeing each medium (reach as a decimal subtracted from 1.0) When these are multiplied they give the net probability of not seeing any of the media. When this result is subtracted from 1, the final result is net reach. This style is particulary useful for combining several media at once.The example would combine this way:  10.4 = 0.6
 10.55 = 0.45
 0.6 x 0.45 = 0.27
 10.27 = 0.73 or
73% reach.
Telmar's "Media Mix" program uses these assumptions.
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