  We revisit identification based on timing and information set assumptions in
structural models, which have been used in the context of production functions,
demand equations, and hedonic pricing models (e.g. Olley and Pakes (1996),
Blundell and Bond (2000)). First, we demonstrate a general under-identification
problem using these assumptions in a simple version of the Blundell-Bond
dynamic panel model. In particular, the basic moment conditions can yield
multiple discrete solutions: one at the persistence parameter in the main
equation and another at the persistence parameter governing the regressor. We
then show that the problem can persist in a broader set of models but
disappears in models under stronger timing assumptions. We then propose
possible solutions in the simple setting by enforcing an assumed sign
restriction and conclude by using lessons from our basic identification
approach to propose more general practical advice for empirical researchers.
