"The following information applies to the coding of the ""licensure"" worksheet."
"A regulation is counted as a ""license"" only if it virtually prohibits a natural person from practicing the occupation without first obtaining permission, which in turn depends on either the discretion of a government body or certain training or educational requirements. Laws that simply provide ""title protection,"" prohibiting use of a certain title without obtaining training or educational requirements, are not counted, except that particularly extreme title protection laws that virtually prohibit uncertified professionals from advertising their practice at all, are counted as licensure. (For instance, a law prohibiting an uncertified person from calling herself a ""certified interior designer"" would not count, but a law prohibiting the same person from calling herself an ""interior designer"" or advertising that she practices ""interior design"" would count.) Mandatory registration that requires only a periodic fee and minimal requirements relating to criteria such as age and noncriminal behavior does not count. Certification and registration programs are noted in comments wherever possible. Business licensing is not considered at all, except to the extent that it effectively applies to an entire class of occupation, such as first-line construction trades managers (contractors)."
"Special note on contractors: Some states license contractors but not their employees. In the occupational statistics, some contractors would show up as ""first-line supervisors"" but others would not, if they do not have employees. So when a state licenses contractors but not journeypersons in an occupation (e.g., fire alarm installers), a code of ""0.5"" is given for that state-occupation."
"All employment data come from the Bureau of Labor Statistics, Occupational Employment Statistics--National Cross-Industry Estimates (http://www.bls.gov/oes/oes_dl.htm), accessed 12/31/2009, 2/13/2012, and 11/11/2014. National rather than state estimates are used, because state occupational estimates are plagued by missing data. Licensed occupations are not generally coded unless they appear to comprise the entirety or the majority of the employment in a particular occupational category recognized by the BLS. Certification and registration are not counted as licensure. State boards' websites and statutes were consulted, as well as national professional association websites in certain cases. For 1984, 1991, and 2003 data, the Book of the States was consulted. For 1993 data, the CLEAR publication, The Directory of Professional and Occupational Regulation in the United States, was consulted. Additionally, the BLS' Occupational Outlook Handbook (http://www.bls.gov/oco/) was consulted for individual occupations. Another source for licensing data is CLEAR News Online (http://clear.blogs.com/). The 2012 Institute for Justice study, License to Work: A National Study of Burdens from Occupational Licensing, https://www.ij.org/licensetowork, was also used. When data from the earlier sources and the IJ report conflicted, state regulatory agency and professional association websites were consulted to resolve differences. In most cases, we adopt the IJ coding, but in a few instances we believe our original codings are superior. State statutes are also routinely consulted."
"A weighted average of each state's licensure prevalence for the coded occupations is obtained by multiplying each state's license score (0, 0.5, or 1) in each year by the occupation's average proportion of total employment in these occupations (see last rows of ""licensure"" sheet)."
Previous versions of this spreadsheet contained some occupations that had mandatory registration in some states but not licensing in any state. This version of the dataset drops those occupations.