Supplementary Materials: The supplementary appendix to this article provides additional results about the method developed in the present article. In particular, Section S1 analyses several extensions of the model analyzed in the main text, including unbalanced panels, observed factors, and consistency of the GMM estimator under an alternative set of assumptions, in which the factor loadings are treated as a sequence of constants. Section S2 provides descriptive statistics for the data used in the empirical illustration. Section S3 reports additional Monte Carlo results. Finally, Section S4 provides proofs of the main theoretical results put forward in the article. The supplemental materials are available online at: https://ndownloader.figs...