Deleting Unreported Innovation
研究了处理企业未报告创新数据的六种方法，发现排除或归零处理会导致参数估计偏误，尤其专利缺失会引发假阳性结果，建议使用多重插补法。
Abstract The absence of observable innovation data for a firm often leads us to exclude or classify these firms as non-innovators. We assess the reliability of six methods for dealing with unreported innovation using several different counterfactuals for firms without reported R&D or patents. These tests reveal that excluding firms without observable innovation or imputing them as zero innovators and including a dummy variable can lead to biased parameter estimates for observed innovation and other explanatory variables. Excluding firms without patents is especially problematic, leading to false-positive results in empirical tests. Our tests suggest using multiple imputation to handle unreported innovation.