The Work Environment Index (WEI) rates working environments in all 50 states and Washington, D.C., in terms of average pay, employment opportunities, employee benefits, percentage of low-income workers, fair treatment between genders and ability for employees to unionize. It is the first index to evaluate worker climate as opposed to business climate on a state-by-state basis, and was developed by researchers at Political Economy Research Institute (PERI) at the University of Massachusetts.