However, because these are demographic variables that hardly vary over the short term, their disaggregate analysis is omitted. The survey year used differs from country to country. The period 1990 refers to the survey nearest to that year, the period 2002, to the survey available nearest to 2000 and 2002, and the period 2008, to surveys available between 2004 and 2008. In the countries that saw the greatest poverty reduction, the workforce grew in tandem with higher labour income per employed person, while in the other countries that was not the case. A simple way to illustrate these differences is to compare the poverty rate of a group of persons with a given trait with others who do not share that trait.