Google housecleaning explains ad drop: comScore

SAN FRANCISCO (Reuters) - Google Inc's ongoing efforts to improve the effectiveness of advertisements it shows viewers is largely responsible for a sharp drop in a key ad sales measure from Web researcher comScore Incthat spooked the market earlier this week, comScore said on Friday.

Internet audience research firm comScore issued a report on Monday showing a 7 percent drop in advertisements viewed on the site during January compared with December, even as Web searches rose 9 percent over the same period.

But on Friday comScore sought to clarify the statistics, pointing out that Google has taken measures over the past year to improve what it terms "ad quality" -- by changing the appearance and frequency of ads running on Google.

"The evidence suggests that the softness in Google's paid click metrics is primarily a result of Google's own quality initiatives that result in a reduction in the number of paid listings and, therefore, the opportunity for paid clicks to occur."

ComScore's discussion of the issue can be found in a blog post on the company's site at tinyurl.com/yt5v5x/.

(Reporting by Eric Auchard; Editing by Richard Chang)