The proportion of Korean households considered middle class has dropped by 3.4 percentage points since 2003, government data showed yesterday.

According to the Ministry of Finance and Strategy and Statistics Korea, middle class households accounted for 66.7 percent of the total last year, dropping by 3.4 percentage points from the 70.1 percent recorded in 2003.

The Finance Ministry said that population aging - which causes the number of one-person households to increase - and rapid technological advancements were the main causes of the decline of the middleclass.

According to Statistics Korea, the proportion one-person households has risen to 20.2 percent from 15.6 percent in 2000. Last year one-person households were the only group to see a decline in average income.

Compared to 2008, however, last year's figure was up by 0.5 percentage point.

The Finance Ministry attributed the year-on-year increase to a general decrease in income brought on by the global economic crisis.

The figures are based on disposable income of households, and exclude those working in the agricultural and fisheries industries, and those composed of a single individual.

A middle class household is defined as one whose income is between 50 percent and 150 percent of the median income. Those making less than 50 percent of the median are categorized as poor, while households whose income is more than 1.5 times larger than the median are classified as upper class.

While the proportion of households in the middleclass fell by 3.4 percentage points, that accounted for by those categorized as poor rose by 1.5 percentage points to come in at 13.1 percent last year.

Over the same period, the proportion of households in the upper class rose by 1.9 percentage points to 20.2 percent, indicating that more middle class households were incorporated into the upper rather than the low-income group during the period.

However, a reverse trend is seen when recent figures are compared to older data.

According to the Korea Development Institute's data, the proportion of such households in the middleclass fell from 75.2 percent in 1992 to 63.3 percent last year.

Over the same period, the proportion of households accounted for by those in the lower income group increased by 6.6 percentage points to 14.3 percent, while that of the upper class rose by 5.3 percent to 22.4 percent.