Editor's note: This article appeared in the November 9, 2009, edition of Quirk's e-newsletter.

While conventional wisdom might suggest that advertisers should try to reach consumers when they have their full faculties available - and not when they are tired and fatigued - research conducted by Derek D. Rucker, associate professor of marketing at the Kellogg School of Management at Northwestern University , Evanston, Ill., suggests this might not be the case.

In particular, during times of the day when consumers are tired or worn out, exposure to advertising can strengthen the confidence consumers have about their attitudes about an advertised brand - and those with positive feelings might be more inclined to make a purchase. The state of feeling tired or run down when exposed to advertising messages is called regulatory depletion.

"Consumers often need to exert substantial psychological resources to manage work-related stress, control impulsive spending and handle financial anxiety," says Rucker. "Undoubtedly, this tires them out. Prior research has suggested that this state of depletion can make a consumer easier to persuade by advertising. In this new research, however, we tested the idea that when people are depleted but are able to process information anyway, the depletion leads them to feel as if they have been more thorough. We found that consumers indeed feel as if they are more thoughtful in their processing when depleted and, as a result, become more firm and confident in their beliefs - positive or negative."

To test the theory, researchers conducted three experiments in which research participants were first put into depleted or non-depleted states and asked to carefully observe advertisements about a cracker snack and toothpaste. Participants noted their attitude and attitude certainty toward the advertised product, and then indicated whether or not they would buy the product. While both groups came to similar opinions about an advertised product, the depleted consumers were more certain about their attitudes, and those with positive outlooks had an increased desire to buy a product as a result of this increased certainty. Thus, marketers with highly-engaging messages might benefit from targeting consumers at times of the day when they are likely to feel depleted, such as in the evening or after work.

However, Rucker noted that depleted consumers are likewise more certain of their negative attitudes. "For marketers, this means that an ad with weaker positioning can actually backfire by directly turning consumers away from a purchase."