When I called him last month to discuss his provocative arguments, he was disarmingly modest. “I’m just an old has-been, I don’t present myself as an expert in this or any other area,” he said.

Image Thomas Siebel saw a plunge in information technology's growth rate. Credit... Lynn Donaldson for The New York Times

The huge difference in growth rates, pre- and post-2000, may seem so stark as to leave no room for an alternative view of I.T.’s prospects.

But the recent drop is not as steep as it seems at first. I asked Shane Greenstein, an economist at Northwestern University’s Kellogg School of Management who has written extensively about the computer industry, to take a look at the raw data upon which those numbers were supposedly based: the annual I.T. spending estimates published by IDC.

Mr. Greenstein’s calculations produced a more moderate compounded annual growth rate of 11.6 percent for 1980 to 2000, instead of 17 percent. (Mr. Siebel’s personal assistant said last week that the 17 percent in the Stanford talk came from a staff member who calculated from a reading of a chart, not from precise figures.)

When Mr. Greenstein looked at the full IDC data set, which goes back to 1961, and used other breakpoints to compare growth in earlier and later periods, he found that the most golden years of I.T. were in the 1960s, when use of mainframe computers spread widely. From 1961 to 1971, the compounded annual growth rate was 35.7 percent, more than three times the rate in the 1980-2000 period celebrated by Mr. Siebel.

Declining growth rates over time are to be expected, Mr. Greenstein said. After all, it doesn’t take many sales to show huge percentage gains when the base is small.

TIMOTHY BRESNAHAN, a Stanford economist, similarly does not accept Mr. Siebel’s contention that the decline in growth rates this decade, which encompasses two recessions, signals a permanent end to I.T.’s record of growing faster than the larger economy. “It is early days to say the game is over,” he said.