Giffen behavior independent of the wealth level

We demonstrate that a well-behaved utility function can generate Giffen behavior, where “well-behaved” means that its indifference curves are smooth, convex, and closed in a commodity space; the resulting demand function of each good is differentiable with respect to prices and income. Moreover, we show that Giffen behavior is compatible with any level of utility and an arbitrarily low share of income spent on the inferior good. This contrasts sharply with the common view that the Giffen paradox tends to occur when households’ wealth levels are low. Comments from Murray C. Kemp, Binh Tran-Nam, Ngo Van Long, Masao Oda, Noritsugu Nakanishi, and Chiaki Hara have greatly improved the paper. We have also benefited from discussions with Koichi Hamada, Satya Das, Takashi Kamihigashi, Tomoyuki Kamo, Toru Kikuchi, Katsufumi Fukuda, Yu-chin Chen, Fahad Khalil, Takeshi Nakatani, Kazuo Nishimura, Ken-Ichi Shimomura, and Stephen J. Turnovsky. We thank the anonymous referee for his/her helpful comments. Iwasa would like to acknowledge financial support from Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists. Professor Koji Shimomura passed away on February 24, 2007. This paper was completed after his untimely death.