Measurement at the level of total sales dilutes the measured ad effect by including all the repeat purchases.

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In theory, this gives the advertiser a better feel for the effect that ad had on those other 999 viewers who did not click on it.

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Changes in the tax code, tighter federal regulations on entertainment practices and the overall decline in print-ad sales have also had an effect.

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You know, you're partnering with someone that in effect competes with you for ad dollars.

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In effect, a cheap banner ad becomes the crummy plastic toy in the Happy Meal.

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With a minimum of investigation, the DOJ could determine that the Google-Mozilla deal is highly analogous in anti-competitive effect to the proposed Google-Yahoo ad agreement that the DOJ blocked in 2008 and is potentially analogous to the tying concerns the DOJ had in its successful Sherman antitrust case against Microsoft.

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Clark Fredricksen, vice president at eMarketer, said it's "tough to speculate" how much effect Thursday's announcement would have on ad revenue.

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Search ad spending was still increasing in Japan, despite the effect of the earthquake and tsunami late in the first quarter.

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It's a lesson that other marketers are undoubtedly heeding as they deal with a new world order of blogs, message boards and interactive ad campaigns, which has accelerated the word-of-mouth effect on consumer products.

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They need to show not just that the ad was shown to a large number of people, but that it actually had some effect on a business metric that the company and its investors care about.

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