The income gap among households reached its widest level ever in 2011, the Health, Labor and Welfare Ministry reported.

The ministry on Friday attributed the expanding disparity mainly to an increase in the number of elderly and single-person households with smaller incomes.

The key parameter for measuring income inequalities, known as the Gini coefficient, came to 0.5536 in the reporting year, up 0.0218 point from the previous study conducted in 2008, before the collapse of Lehman Brothers Holdings Inc. sent the global economy into a tailspin.