A famous New Yorker cartoon from 1993 showed two dogs at a computer, with one saying to the other, “On the Internet, nobody knows you’re a dog.”

That may no longer be true.

A new analysis of online consumer data shows that large Web companies are learning more about people than ever from what they search for and do on the Internet, gathering clues about the tastes and preferences of a typical user several hundred times a month.

These companies use that information to predict what content and advertisements people most likely want to see. They can charge steep prices for carefully tailored ads because of their high response rates.

The analysis, conducted for The New York Times by the research firm comScore, provides what advertising executives say is the first broad estimate of the amount of consumer data that is transmitted to Internet companies.