Reasons why workers are often paid more than they could make in their best alternative positions do not include: (1) human capital valued by many firms. (2) membership in a union along with a labor contract. (3) holding a minimum wage job when most unskilled workers are unemployed. (4) important specific training that the firm wants to retain. (5) efficiency wages which firms pay to reduce moral shirking (hazard).
Can anybody suggest me the proper explanation for given problem regarding Economics generally?