Biggeri and Mehrotra have studied the macroeconomic factors that encourage child labour. They focus their study on five Asian nations including India, Pakistan, Indonesia, Thailand and Philippines. They suggest that child labour is a serious problem in all five, but it is not a new problem. Macroeconomic causes encouraged widespread child labour across the world, over most of human history. They suggest that the causes for child labour include both the demand and the supply side. While poverty and unavailability of good schools explain the child labour supply side, they suggest that the growth of low-paying informal economy rather than higher paying formal economy is amongst the causes of the demand side. Other scholars too suggest that inflexible labour market, sise of informal economy, inability of industries to scale up and lack of modern manufacturing technologies are major macroeconomic factors affecting demand and acceptability of child labour.