Obtaining reliable measures of firm creation, survival, and growth is a challenge in any setting but is particularly important and problematic in the transitional countries in East Central Europe. The research reported here is based on a unique dataset prepared jointly with the Research Center for Economic and Statistical Studies of the Polish Central Statistical Office. These data constitute a longitudinal file on the employment, payroll, and sales of firms existing in Poland between 1990 and 1997. This longitudinal dataset is based on the information that firms are required to report to the Central Statistical Office on an annual basis. They have an obvious limitation, however, in that they exclude information on firms that chose not to report or that were not required to report. The first category, those who chose not to report information, covers the so-called gray economy, which was very much in evidence in these countries, although it may be shrinking, in Poland at least (Dzierżanowski, 1999, p. 31). The second category constitutes a more serious concern for this research. In Poland, firms employing five or fewer workers are exempt from filing annual reports with the statistical office. The consequences of this omission could be substantial, as this sector is large, possibly employing as many as 2 million people, and constitutes the critical early stage of the entrepreneurial process. In this extended appendix we want to explore the possible statistical consequences of this omitted information.