  This note provides a critical discussion of the \textit{Critical
Cost-Efficiency Index} (CCEI) as used to assess deviations from
utility-maximizing behavior. I argue that the CCEI is hard to interpret, and
that it can disagree with other plausible measures of "irrational" behavior.
The common interpretation of CCEI as wasted income is questionable. Moreover, I
show that one agent may have more unstable preferences than another, but seem
more rational according to the CCEI. This calls into question the (now common)
use of CCEI as an ordinal and cardinal measure of degrees of rationality.
