However clear-cut the differences between the theories may be, direct tests of these issues lead to no very clear conclusions.

If it's Bradley versus George W. Bush, it's easy because there are such clear-cut differences.

"It's a pretty clear-cut difference," Mr. Blackwelder said.

But it now seems to be established that there is no clear-cut difference in the role of environmental factors in so-called 'neurotic' or 'psychotic'depressions (see Paykel et al., 1984).

But many lawyers, even those who have sued Merck on behalf of patients who took Vioxx, said yesterday that there are clear-cut differences.

"I don't think we've had as clear-cut a difference between two presidential candidates on international issues since 1980," said Richard C. Holbrooke, a former United Nations ambassador and now a top adviser to Mr. Kerry.

Despite the clear-cut differences between the candidates on the debate issue, their agents decided to resume negotiations here on Thursday, an indication to some that they might be closer to agreement than they appeared.

And we can't formulate a clear-cut difference between sane and insane.

In practice, however, the distinction is not concrete, as there is no clear-cut difference between factual, "encyclopedic" information and linguistic information such as appears in dictionaries.

Nevertheless, the data showed a clear-cut difference between stutterers and controls.