This theory suggests there are two sets of factors that impact upon an employee's feelings of satisfaction at work. The first set (hygiene factors) concerns the employee's need for fair treatment in compensation, supervision, and working conditions. If these are not met, employees feel dissatisfied. However, if managers devise ways of meeting these needs, it will still not lead to job satisfaction. In addition, a second set of needs (motivator factors) concerning personal growth and development in the job (promotion, achievement, responsibility, etc.) must be met for employees to experience job satisfaction. The distinction between these two sets of factors is important because it means that different factors are responsible for job satisfaction and job dissatisfaction. The theory was developed by psychologist, Frederick Herzberg, in the 1960s and had an influence on methods of job redesign. Critics argue that the theory is inadequate because it does not take into account situational variables, the measures of satisfaction are questionable, and it tends to assume that job satisfaction will lead to improvement in productivity.