I would say that this statistic probably refers to the richest countries where the standard of living is higher than poor countries and if it was infant mortality then more modern health facilities and access to them would be a strong factor hopefully better in the countries with a higher standard of living. On the other hand, Cuba has an infant mortality of 4.76 deaths per 1000 live births compared to 5.90 for the US so is a testament to the success of their social system.
