Here is the basic result Kristof is talking about:
Arthur Brooks, the author of a book on donors to charity, “Who Really Cares,” cites data that households headed by conservatives give 30 percent more to charity than households headed by liberals. A study by Google found an even greater disproportion: average annual contributions reported by conservatives were almost double those of liberals.
Rather than taking that at face value, several questions should immediately pop into your mind:
1. Is this because more conservatives go to church, and give moeny to their church? For example, Mormons (who tend to be conservative), give 10% of their income to one of the wealthiest churches on the face of the planet, and one which does considerably less humanitarian work around than many churches (liberal and conservative) with much less wealth. Most of us wouldn't count everything you give to your church as "giving to charity," so you should ask yourself if the studies Kristof talks about take church giving into account.
And in fact, Kristof notes that "According to Google’s figures, if donations to all religious organizations are excluded, liberals give slightly more to charity than conservatives do."
But maybe that's because conservatives are already giving a big chunk of change to their church (which may really go to substantial charitable work, and not just to the general operating expenses of the church), so there is less money left over to give to non-religious charities. Thus excluding "donations to all religious organizations" may not be a fair comparison either.
2. Are conservatives richer, and thus able to give more to charity? Kristof notes that "measuring by the percentage of income given, conservatives are more generous than liberals even to secular causes," but we're given no information on how giving relates to wealth. When I'm spending 80% of my income on basics like food, housing, and transportation, I have less money to give as a percentage of my income. If I only spend 30% on the basics, I'm free to give a larger chunk to charity.
3. How much is related to say, issues of urban vs. rural environments, instead of liberal/conservative? One claim is "People in red states are considerably more likely to volunteer for good causes, and conservatives give blood more often." Is that because there are more volunteer opportunities in smaller towns than in big cities? I grew up outside of the fairly small city of Ithaca, NY. I volunteered for the local fire department there, something I could never do now in St. Louis because the fire department is all professional.
There are obviously more questions to ask, and it's not clear at all, at least from the newspaper story, what we should really believe. It may very well be that, once you control for all of the confounding factors, liberals really are stingier. At least as Americans we're giving 11 times more of our GNP to charity than the French, as Kristof notes.
But wait - the French pay a lot more in taxes to provide many services which are provided by charities in the US. So who really is more generous?
I'm not taking a stand on what the right answer is to any of these comparisons. The lesson here is, don't just believe the headline for any study. Learn to ask the right questions.