Occupational licensing law research project (OLLRP)
Welcome to the first installment of our data project. This database was sourced and compiled by Morris Kleiner, Jason Hicks, Corissa Marson, Ethan Ellis, Evan Cunningham, and 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.
Sponsorship for this project 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 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. His paper "Historical Data on Professional and Occupational Credentialing Requirements in the United States" can be found here, as well as his GitHub page 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.
- 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.
- 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
See table below to find the downloadable data dictionary file (row 1).
June 2025: Version 1 Database***
| Profession | Read.Me File Download | Universally Licensed? | Data Download File |
Data Dictionary File |
Data.Dictionary | ||
Cosmetologist |
Cosmetology.ReadMe |
Partially |
Cosmetologist.Data |
Dispensing Optician |
Dispensing.ReadMe |
Partially |
DispensingOpt.Data |
Licensed Practical Nurse |
LPN.ReadMe |
Partially |
LPN.Data |
Massage Therapist |
Massage.ReadMe |
Partially |
Massage.Data |
Professional Counselor |
Counselor.ReadMe |
Partially |
Counselor.Data |
Respiratory Therapist |
Respiratory.ReadMe |
Partially |
Respiratory.Data |
Optometrist |
Yes |
Optometrist.Data | |
Physician Assistant |
Yes |
PA.Data | |
Physician |
Yes |
Physician.Data | |
Registered Nurse |
Yes |
***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, and Nicholas Carollo. "Occupational Licensing Law Research Project", Knee Regulatory Research Center, West Virginia University, 2025.
Find Archived Data for Download Here:
Citations:
Carollo, Nicholas. "Historical Data on Professional and Occupational Credentialing Requirements in the United States." Available at SSRN 3687130 (2020).
Kleiner, Morris, M. Jason Hicks, Corissa Marson, Ethan Ellis, Evan Cunningham, and Nicholas Carollo. "Occupational Licensing Law Research Project", Knee Regulatory Research Center, West Virginia University, 2025.