Abstract A screening instrument is costly if it is socially wasteful and productive otherwise. A principal screens an agent with multidimensional private information and quasilinear preferences that are additively separable across two components: a one-dimensional productive component and a multidimensional costly component. Can the principal improve upon simple one-dimensional mechanisms by also using the costly instruments? We show that if the agent has preferences between the two components that are positively correlated in a suitably defined sense, then simply screening the productive component is optimal. The result holds for general type and allocation spaces, and allows for nonlinear and interdependent valuations. We discuss applications to monopoly pricing, bundling, and labour market screening.

A nested bundling strategy creates menus in which more expensive bundles include all the goods of less expensive ones. We study when nested bundling is optimal and determine which nested menu is optimal, when consumers differ in one dimension. We define a partial order on bundles by (i) set inclusion and (ii) sales quantity when sold alone. We show that, under quasi-concavity assumptions, if the undominated bundles with respect to this partial order are nested, then nested bundling is optimal. We present an iterative algorithm that identifies the minimal optimal menu consisting of a subset of the undominated bundles. (JEL D11, D21, D42, D82, M31)