Wage differences across markets can be linked to labor supply and labor demand. Some jobs pay more than others because they require a long, costly training period. This makes the supply of those individuals willing to go through the training fewer. The training that the individuals receive increases their productivity and that increases the demand for their skills. This lower supply of individuals coupled with the increased demand for their skills drives the wage up.
Some individuals earn more because they are more able and more talented.
Difference in Risk Jobs that have a higher probability of injury or death pay more. Geographic Differences People have an incentive to sell their labor in a market where they can earn the most. Job Discrimination Your sex or race may cause you to earn more or less. This is illegal, but it can happen. It is a skill difficult to teach and difficult to measure.