My late mentor, Nobel Prize-winning economist George Stigler, used to say that it could be very instructive to spend a few hours in a library checking up on studies that had been cited. When I began doing that, I found it not only instructive but disillusioning.

A footnote in a textbook on labor economics cited six studies to back up a conclusion it reached. But, after I went to the library and looked at those six studies, it turned out that they each cited some other study — the same other study in all six cases.

Now that the six studies had shrunk to one, I got that one study — and found that it was a study of a very different situation from the one discussed in the labor economics textbook.

Some years back, there was a great flurry in the liberal media because a study showed that (1) black pregnant women received prenatal care less often than white pregnant women and that (2) infant mortality rates were higher among blacks.

There were indignant editorials in the New York Times and the Washington Post blaming the government for not providing greater access to prenatal care in order to stop preventable deaths of infants.

After getting a copy of the original study, I discovered that in the same study — on the very same page — statistics showed that (1) Mexican American women received even less prenatal care than black women and that (2) infant mortality rates among Mexican Americans were no higher than among whites.

A few pages further on, statistics showed that American women of Chinese, Japanese and Filipino ancestry also received less prenatal care than white women — and had lower infant mortality rates than whites.

Apparently prenatal care was not the answer, though it was the kind of answer that suited the mindset of the liberal media and provided an occasion for them to wax indignant.

More recently, the National Academy of Sciences came out with a study that supposedly proved beyond a doubt that human activities were responsible for “global warming.” A chorus of voices in the media, in politics and in academia proclaimed that this was no longer an issue but a scientific fact, proven with hard data.

The NAS report not had only statistics, it had an impressive list of scientists, which supposedly put the icing on the cake.

The only problem was that the scientists had not written the report and in fact had not even seen it before it was published, even though they had some affiliation with the National Academy of Sciences.

At least one of those scientists, meteorologist Richard S. Lindzen of M.I.T., publicly opposed the conclusion and has continued to do so. But that fact was largely lost in the midst of the media hoopla.

Besides, what is a mere meteorologist at M.I.T. compared to Al Gore and his movie?

Nobody can afford the time to check out every claim of what “studies prove.” Even with the help of outstanding research assistants, I can only check out some.

However, the big television and print media have ample financial resources to check out claims before they present them to the public as “news.” But when “60 Minutes” didn’t bother before basing a story about President Bush’s national guard service on a forged document, do not look for a lot of zeal for facts when that could kill a juicy story or the political spin accompanying it.

Let’s face it. There is not much pay-off to checking original sources.

Once a minister was explaining to me the structure of his funeral orations. He said, “At this point, you are expected to say something good about the deceased. Now, Tom, if I were preaching your funeral, what would I say good about you at that point?”

He thought and thought — for an embarrassingly long time. Finally, he said gravely: “In his research, he always used original sources.”

I’ll take that.

To find out more about Thomas Sowell and read features by other Creators Syndicate columnists and cartoonists, visit the Creators Syndicate web page at www.creators.com. Thomas Sowell is a senior fellow at the Hoover Institution, Stanford University, Stanford, CA 94305. His Web site is www.tsowell.com.