Examining Geico, Mr. Wilt found it to have customers with disproportionately higher income and education, and more receptivity to technology. Geico, based in Chevy Chase, Md., is a subsidiary of Berkshire Hathaway.

The analyst said Geico demonstrates how insurers have joined the big leagues of advertising.

Mr. Wilt wrote that Geico's $500 million ad spend last year was greater than that of Coca Cola USA, while Progressive spent twice as much as Citibank.

He found that Geico's saturation television advertising has more than proved its value. While it currently spends 58 percent more than Allstate on television ads, their effectiveness rate by one metric is 6.5 times greater, he wrote.

"What can we say, the Gecko works, even for reasons we don't understand," Mr. Wilt wrote of the animated lizard who appears as the company spokesman in its televised ads.

Mr. Wilt opined that Geico, with its tech-savvy customer base, may be under-spending on Internet advertising. Geico policyholders both use and trust the Internet as media outlet in greater proportion than the company at large, he reported.

For the overall auto insurance market, Mr. Wilt said the era of sophisticated underwriting-ratemaking techniques as a greater market differentiator "seems to be evaporating faster than we had envisioned."

In addition, he wrote that cross-selling no longer appears to be the road to top-line riches. "The market of people willing to purchase single products from single companies is apparently bigger than we had believed," Mr. Wilt wrote. "This is good news for Geico and Progressive."