More frightening than any particular beliefs or policies is an utter lack of any sense of a need to test those beliefs and policies against hard evidence. Mistakes can be corrected by those who pay attention to facts but dogmatism will not be corrected by those who are wedded to a vision.

One of the most pervasive political visions of our time is the vision of liberals as compassionate and conservatives as less caring. It is liberals who advocate "forgiveness" of loans to Third World countries, a "living wage" for the poor and a "safety net" for all.

But these are all government policies -- not individual acts of compassion -- and the actual empirical consequences of such policies are of remarkably little interest to those who advocate them. Depending on what those consequences are, there may be good reasons to oppose them, so being for or against these policies may tell us nothing about who is compassionate or caring and who is not.

A new book, titled "Who Really Cares" by Arthur C. Brooks examines the actual behavior of liberals and conservatives when it comes to donating their own time, money, or blood for the benefit of others. It is remarkable that beliefs on this subject should have become conventional, if not set in concrete, for decades before anyone bothered to check these beliefs against facts.

What are those facts?

People who identify themselves as conservatives donate money to charity more often than people who identify themselves as liberals. They donate more money and a higher percentage of their incomes.

It is not that conservatives have more money. Liberal families average 6 percent higher incomes than conservative families.

You may recall a flap during the 2000 election campaign when the fact came out that Al Gore donated a smaller percentage of his income to charity than the national average. That was perfectly consistent with his liberalism.

So is the fact that most of the states that voted for John Kerry during the 2004 election donated a lower percentage of their incomes to charity than the states that voted for George W. Bush.

Conservatives not only donate more money to charity than liberals do, conservatives volunteer more time as well. More conservatives than liberals also donate blood.

According to Professor Brooks: "If liberals and moderates gave blood at the same rate as conservatives, the blood supply of the United States would jump about 45 percent."

Professor Brooks admits that the facts he uncovered were the opposite of what he expected to find -- so much so that he went back and checked these facts again, to make sure there was no mistake.

What is the reason why some people are liberals and others are conservatives, if it is not that liberals are more compassionate?

Fundamental differences in ideology go back to fundamental assumptions about human nature. Based on one set of assumptions, it makes perfect sense to be a liberal. Based on a different set of assumptions, it makes perfect sense to be a conservative.

The two visions are not completely symmetrical, however. For at least two centuries, the vision of the left has included a belief that those with that vision are morally superior, more caring and more compassionate.

While both sides argue that their opponents are mistaken, those on the left have declared their opponents to be not merely in error but morally flawed as well. So the idea that liberals are more caring and compassionate goes with the territory, whether or not it fits the facts.

Those on the left proclaimed their moral superiority in the 18th century and they continue to proclaim it in the 21st century. What is remarkable is how long it took for anyone to put that belief to the test -- and how completely it failed that test.

The two visions are different in another way. The vision of the left exalts the young especially as idealists while the more conservative vision warns against the narrowness and shallowness of the inexperienced. This study found young liberals to make the least charitable contributions of all, whether in money, time or blood. Idealism in words is not idealism in deeds.