The earned income of South Korean households headed by 40-somethings posted the sharpest drop ever in the fourth quarter of last year since such data has been compiled.

According to Statistics Korea on Saturday, the earned income of domestic households headed by people in their 40s fell more than three percent from a year ago to three-point-four million won during the October to December period of last year.

A number of factors contributed to the sharp plunge including the sluggish restaurant and accommodation sectors, and youth unemployment bringing down income levels for unmarried members of households.

The earned income of this demographic, considered the backbone of South Korean society, consistently grew between 2003 and 2016 with the exception of the third quarter in 2009 during the global financial crisis when the figure fell two-point-nine percent.

The earned income of households led by 40-somethings recorded its second drop of one-point-three percent in last year's second quarter and further declined by three-point-one percent in the fourth quarter.