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Knee Regulatory Research Center
John Chambers College of Business and Economics
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OLLRP Database

The Occupational Licensing Law Research Project Database

occupations and regulation


Occupational licensing law research project (OLLRP)


Welcome to the first installment of our data project. This database was sourced and compiled by Dr. Morris Kleiner, Dr. Jason Hicks, Corissa Marson, Ethan Ellis, Evan Cunningham, Dr. Wenchen Wang, and Dr. Nicholas Carollo, with generous financial support from the many sponsors listed below. This is the first installment of a longitudinal, historical project set out by the original authors which will now be updated and managed by researchers at the KRRC. 
Spo nsorship for this p roject include the following institutions: 
Smith Richardson Foundation
Russell Sage Foundation
Charles Koch Foundation
Federal Reserve Bank of Minneapolis
Washington Center for Equitable Growth
Hoover Institution, Standford University
Humphrey School of Public Affairs, University of Minnesota
National Bureau of Economic Research
W.E. Upjohn Institute for Employment Research
The Hamilton Project, Brookings Institution
Minnesota Population Center (MPC), University of Minnesota
The Institute for Humane Studies at George Mason University
Ewing Marion Kauffman Foundation
The Knee Regulatory Research Center 

This project is a success with many thanks and data support from Nicholas Carollo, senior economist in the Labor Markets section of the Division of Research and Statistics at the Federal Reserve Board of Governors. Carollo's paper "Historical Data on Professional and Occupational Credentialing Requirements in the United States" can be found here, as well as his GitHub page (2025), where you can find raw data and Stata code for almost 300 occupations or license categories throughout all 50 states and DC, covering most policies enacted from 1870 to 2019 for these occupations.

You will find below “universally licensed” and “partially licensed” occupations. The universally licensed data variables are a subset of the variables you will find in the data dictionary.

The following occupations are now available:

Partially Licensed:

  • Cosmetologists
  • Dispensing Opticians
  • Licensed Practical Nurse
  • Massage Therapist
  • Professional Counselor
  • Respiratory Therapist
The partially licensed data includes all variables from the data dictionary and covers all pathways and requirements within the scope of this project.

Universally Licensed:

  • Optometrist
  • Physician Assistant
  • Physician
  • Registered Nurse
The universally licensed data variables are a subset of the variables you will find in the data dictionary. The data assumes required education is fixed at its lowest level, and records other requirements given that assumption.

Upcoming occupations:

  • Funeral Director
  • Embalmer
  • Nursing Assistant
  • Interior Designer
  • Marriage and Family Therapist
  • Barber
Future additions to this database include:
  • Code for a data walk-through
  • Forthcoming methodology paper

Note for use: Be sure to download and read both universal and partially licensed occupations' data dictionary and read me files below (rows 1 & 2).

June 2025: Version 1 Database**

Profession Read.Me File Licensed Type Data Download File
PARTIALLY LICENSED Download by occupation below Partially licensed Partial.Data.Dictionary
UNIVERSALLY LICENSED Universal.Read.Me Universally licensed ALL OCCUPATIONS Universal.Data.Dictionary
Cosmetologist Cosmetology.ReadMe Partially Licensed Cosmetologist.Data
Dispensing Optician Dispensing.ReadMe Partially Licensed DispensingOpt.Data
Licensed Practical Nurse LPN.ReadMe Partially Licensed LPN.Data
Massage Therapist Massage.ReadMe Partially Licensed Massage.Data
Professional Counselor Counselor.ReadMe Partially Licensed Counselor.Data
Respiratory Therapist Respiratory.ReadMe Partially Licensed Respiratory.Data
Optometrist Refer to Row 2* Universally Licensed Optometrist.Data
Physician Assistant Row 2* Universally Licensed PA.Data
Physician Row 2* Universally Licensed Physician.Data
Registered Nurse Row 2* Universally Licensed RN.Data
*All universally licensed occupations' read me file can be found in the "Universal.Read.Me" download. Partially licensed occupations have a read.me file for each occupation individually. 

**Database may be adjusted for error or miscalculation in future versions. Any new versions of database uploads will be posted on a regular basis, while older versions will be available for download in the archived data at the bottom of this page.


Citation for Data Use:  Kleiner, Morris, M. Jason Hicks, Corissa Marson, Ethan Ellis, Evan Cunningham, Wenchen Wang, and Nicholas Carollo. "Occupational Licensing Law Research Project", Knee Regulatory Research Center, West Virginia University, 2025. 

Additional Citations:
Carollo, Nicholas. "Historical Data on Professional and Occupational Credentialing Requirements in the United States." Available at SSRN 3687130 (2020).
Other Archived Data Versions: 

  • Version 1 minor revisions made to remove misleading variables and comments, and add clarifying notation, on Oct. 7, 2025. Any changes made are tracked in the Universal.Read.Me document. Reach out to kneecenter@mail.wvu.edu for first version database files, if necessary.

Feedback is greatly appreciated! We want to hear thoughts and insights on what you are using these data for, what else you might want to see from this work, and any inaccuracies you spot in the database.  Please reach out to  kneecenter@mail.wvu.edu with any feedback or questions regarding the OLLRP database.