MEXICO CITY (Reuters) – Anyone investing in funds linked to Mexico’s IPC stock index in 2011 would have lost nearly double their money had it not been for the gains of a little-known company whose shares rarely change hands.

Grupo Elektra’s stock almost tripled in a year when Mexico’s share index fell, making the company the country’s third biggest by market value – thanks largely to a financial trick that had nothing to do with its discount retail or banking businesses.

The gains recorded by the company, owned by billionaire television magnate Ricardo Salinas, were the biggest of any firm in Brazil, Mexico or Argentina in 2011. Without changes to stock index rules, analysts fear it could further distort Mexico’s IPC index or the widely used MSCI Latin America and MSCI Mexico indices.

Shares in Elektra, which offers Mexico’s poor loans for washing machines and other consumer items, surged 165 percent to 1385.72 pesos from 522.85 pesos a year earlier – despite the fact that sales were up only a quarter of that.

“It does not help Mexico at all to have this sort of behavior in the index,” said Stacy Steimel, managing director and head of Latin America equities at PineBridge Investments. “This does not enhance our appetite for Mexico.”

Mexico’s equity market has lagged its rival Brazil in new public offerings and has struggled to attract investment. The stock market capitalization is about 30 percent of Mexican gross domestic product, next to some 50 percent for Brazil.

Elektra’s price rise was powered by two things: methodology changes that increased its importance in Mexico’s benchmark IPC index, and a derivative instrument known as an equity swap that allows the company to monetize its share-price gains.