A difficulty in the search for Giffen behavior

Gilley and Karels [1991] argue that economists should search for Giffen goods in cases where two or three goods are chosen subject to two constraints. This paper reconsiders their three-good model. With a third good added, traditional comparative statics analysis, which is absent from the simpler model, becomes crucial. The Slutsky equation with a negative own substitution effect reappears, suggesting that one good which is automatically Giffen in the two-good, two-constraint model may have a downward-sloping demand curve when the third good is added to the model.