Before revision:  Under our procedure the researcher achieves robust confidence sets using a priori bounds on the deviation from instrumental validity and approximation error. Our procedure is based on the sieve-minimum distance method and has an added advantage in that it reduces the need to choose the size of the sieve space either directly or algorithmically. We also present a related method that allows the researcher to assess the sensitivity of their NPIV estimates to misspecification.
After revision:  Under our procedure the researcher achieves robust confidence sets using a priori bounds on the degree of misspecification. Our proposed technique is a practical alternative to standard NPIV estimation and allows the researcher to assess the sensitivity of their NPIV estimates to misspecification.