ComScore subsequently backed off its claims a bit, publishing a blog post called “Why Google’s surprising paid click data are less surprising” which explained that the decline in Google’s paid clicks it charted could have been the result of the company’s click-quality initiatives and not a slowdown in its business. But on Tuesday, comScore published another report that showed growth in paid search clicks is slowing. One of its key data points: Google’s paid clicks grew by just 1.8% year-over-year.

Well, Google reported earnings yesterday and according to its metrics, paid-click growth grew by about 20%. And CEO Eric Schmidt did not let that discrepancy between those two figures go unremarked: “The business model continues to work very well,” he said. “It’s also interesting to note that paid-clicks growth is much higher than has been speculated by third parties.”

“Third parties” in this case being comScore. Now, granted comScore’s metrics included U.S. clicks alone, while Google’s included worldwide clicks, so comScore’s estimate, in all likelihood, isn’t off by 18.2%. That said, it’s still off according to Google–which, with that one little quip from Schmidt, sent comScore’s shares down more than 7%, the same decline it suffered at the research outfit’s hands back in February.

Net income rose 31% on revenue growth of 42% from a year ago, exceeding Wall Street estimates. Overall paid clicks rose 20% in the quarter compared with the period a year earlier. That’s down from 30% growth of the previous quarter, but better much better than the forecasts of, ahem, certain third parties. “Our ongoing innovation in search, ads and apps helped drive healthy growth globally across our product lines, yielding another strong quarter for Google,” said Chief Executive Eric Schmidt. Apparently, the slowing U.S. economy hasn’t had much impact on the company’s business.

Shares of Google soared past the $500 mark in after-hours trading on the news. Seems the company’s historic run is far from over.

The collectibles retailer claims it paid Yahoo’s Search Marketing unit, formerly known as Overture Services, some $936,000 between 2002 and 2006 for click-throughs. It assumed these click-throughs were from legitimate customers, but it turned out they were generated by Yahoo/Overture affiliates who received commissions based on the number of clicks their sites generated for advertisers.

“These clicks were not actual traffic, but were fraudulent clicks,” BigReds claims in the suit. “Affiliates of Overture used software programs, employed people, and/or directed people other than actual customers to click on plaintiffs’ links from keyword search results.”

To be fair, Yahoo did offer BigReds a refund for the fraudulent clicks. It just wasn’t as large as the retailer had hoped–$17,082.80.

In a blog post today, comScore CEO Magid Abraham and senior VP James Lamberti argue that the decline in paid clicks is likely the result of improvements in Google’s click programs. “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,” the two wrote. “In addition, the reduction in the incidence of paid listings existed progressively throughout 2007 and was successfully offset by improved revenue per click. … Separately, there is no evidence of a slowdown in consumers clicking on paid search ads for rest of the U.S. search market.”

What’s more, the comScore execs write, Google’s click-quality initiatives don’t necessarily translate into more clicks. “If the ads are more relevant, consumers would need fewer clicks to get what they are looking for,” they explain. “Perversely, a high number of clicks means that the ads are not delivering what the user is looking for on the first try, which induces additional clicks on the second or third try. The benefits to marketers are real, but also counterintuitive. If the users get to what they want with fewer clicks, it means those clicks have a higher conversion rate, or deliver higher quality leads.”

Ah. Well, if that’s the case, why didn’t you say so in the first place? Or at least before you singlehandedly knocked 7% off the company’s share price.

Perhaps the slowing economy is having an impact on Google’s growth after all. Certainly the continued deceleration in the company’s paid click growth suggests as much. In October of 2007 Google showed 37% click growth. In November it showed 27%. Then in December it showed 12%. And in January it showed no growth at all. As Henry Blodget notes over at Silicon Alley Insider, that sort of steady decline seems more a trend than “a wacky one-month comScore aberration.”

Google shares are down more than $34, or about 7%, at $451 as I write this.