Defining the size of Mexico’s middle class is more complicated than it is in the United States, where it is a more straightforward measure of family size and income, with data gathered by the U.S. Census Bureau and other sources.

Mexico is far less transparent country. So economists have measured the country’s middle class by other means — access to household goods or health care, consumption levels, access to credit, education, food security. It’s a politicized statistic, because Mexican politicians and commentators tend to pick the yardsticks that best suit their agendas, depending on whether they want to depict the country as better off, or mired in poverty.

But the expansion of Mexico’s middle class over the past several decades is an undeniable trend, even as the country has been buffeted recently by the global recession.

In 1960, some 80 percent of Mexicans were living in poverty, as defined by what social scientists call “patrimonial poverty” — having sufficient income for food, education and health care, but not enough for clothing and needed household goods. Today that figure has dropped to 48 percent, according to Mexican government data. The population of Mexicans who are “food poor” is about 18 percent.

While Mexico’s inequality gap remains wide compared with more developed countries in Europe and Asia, it has not increased in recent years as rapidly as it has in the United States. Meanwhile, Mexico’s working class appears to be floating upward on a rising tide: GDP per capita has increased from $7,357 in 1990 to $13,928 in 2010, accounting for inflation, according to International Monetary Fund data.

The Organization of Economic Cooperation and Development, a club of 34 developed economies, considers Mexico 50 percent middle class, based on median incomes.

Then there’s another gauge: self-perception. According to the latest surveys, 65 percent of Mexicans see themselves as “middle class” today.