@inbook{NBERc7917,
 Crossref = "NBERfree88-1",
 title = "Appendix B The NBER Public Sector Collective Bargaining Law Data Set",
 author = "Robert Valletta and Richard B. Freeman",
 BookTitle = "When Public Sector Workers Unionize",
 Publisher = "University of Chicago Press",
 pages = "399-420",
 year = "1988",
 URL = "http://www.nber.org/chapters/c7917",
}
@book{NBERfree88-1,
 title = "When Public Sector Workers Unionize",
 author = "Richard B. Freeman and Casey Ichniowski",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "1988",
 URL = "http://www.nber.org/books/free88-1",
}