How changes in demand and supply, relative bargaining strengths, discrimination and government policy can all influence differences in earnings between workers whether they are: skilled/unskilled; primary/secondary/tertiary; male/female; private sector/public sector.

The nature and causes of changes in the pattern of employment, for example increase in proportion of workers employed in the tertiary sector and formal economy as an economy develops; a greater proportion of women in the labour force due to changes in social attitudes; decline in the proportion employed in the public sector as a country moves towards a market economy.