Here’s my Q&A column from the WSJ this week — and if you have any questions for me, you can tweet them to @danariely with the hashtag #askariely, post a comment on my Ask Ariely Facebook page, or email them to AskAriely@wsj.com.

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Dear Dan,

I shop at two different grocery stores. One charges a nickel for paper bags, while the other gives me a nickel when I bring my own bag. Which approach is more likely to reduce paper-bag use?

—Paul 

The general question you’re raising is whether punishment or reward is better at motivating us to change our behavior. Punishments are very powerful for motivating people to do something that they only have to do once—for example, installing a smoke alarm in their house or immunizing their children.

But when it comes to repeated behaviors, positive rewards are more effective. In a study conducted in a New York hospital in 2011, researchers found that when physicians were given positive feedback for washing their hands regularly, compliance with the hospital’s handwashing policy rose from 10% to 90%. I suspect that the same principle would hold here: Offering shoppers a credit for bringing their own bag should yield better results.

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Dear Dan,

Religion is supposed to make people behave better, but do more religious societies actually have less unethical behavior and crime?

—Chad 

I wish it was that simple. Research suggests that religion can play an important role in fostering ethical behavior, but its effects aren’t consistent across the board. A recent paper in the journal Psychological Science examined crime data from 1945 to 2010 for over 170 countries and found that as religious affiliation went down, homicide rates tended to go up—but only in areas with relatively low aggregate intelligence scores. How causation works among these variables isn’t clear, but I suspect that areas with higher intelligence scores are more likely to have institutions such as schools and community organizations that help to foster ethical behavior. So while religion isn’t the only factor, some kind of strong social institutions are crucially important for curbing our worst impulses.

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Hi, Dan.

We all know that we’re going to die one day, but most people don’t prepare wills or make guardianship plans for their children. Is there a way to motivate people to take estate planning seriously?

—Shani 

Making a will forces us think about an event that we don’t want to imagine, to make complex decisions we prefer not to deal with, and to plan for something that feels very far away. All these factors encourage us to procrastinate. But while we experience painful feelings when we think about estate planning, the pain for our survivors is much larger if we don’t make a will.

My research lab at Duke works with a startup called GivingDocs that tries to overcome these obstacles. Before making a will, it asks people to think about the legacy they want to leave behind and the causes they care about, then helps them to plan bequests to the charities that matter to them. This general approach—combining a painful act with distant results, like creating a will, with something that’s immediately meaningful, like donating to charity—is a good way to get people to overcome their tendency to procrastinate.

See the original article in the Wall Street Journal.