Preferences such that a mixture of two equally valued outcomes is at least as good as either of the individual outcomes. If preferences are strictly convex then the mixture is strictly preferred. Formally, assume that outcome x is equally valued to outcome y, and define the mixture z by
z = λx + (1 − λ)y.
Then the preferences are convex if z is at least as good as x for any λ such that 0 ≤ λ ≤ 1. The preferences are strictly convex if z is strictly preferred to x for any λ such that 0 < λ < 1.