The number of single men in their 40s has risen drastically. According to the September issue of Labor Review published by the Korea Labor Institute on Monday, the ratio of 40-year-old single men rose from a mere 1.4 percent in 1985 to 14.8 percent in 2010, meaning 1.5 out of every 10 are unmarried.

Among 45-year-old men, the proportion of singles rose from 0.2 percent in 1985 to 7.7 percent in 2010, and among 49-year olds from 0.3 percent to 4.4 percent.

Those with no education beyond a high school diploma accounted for 22 percent of all single men in 2010. Only 4.3 percent of unmarried men had a college or higher degree, indicating that those with the least education are likely to get married later or not at all.

There is also a connection with poverty. Among unemployed men in their 40s, singles made up 27.4 percent in 2010.

Meanwhile, the proportion of singles among 40-year old women rose from 1.1 percent in 1985 to 7 percent in 2010; among 45-year olds from 0.7 percent to 3.1 percent; and among 49-year olds from 0.3 percent to 1.2 percent.

But overall the proportion of singles among women in their 40s was less than half that of their male counterparts in 2010. In contrast to men, a greater proportion of women with college or higher academic background were unmarried.

"The data show that men who are underprivileged in the labor market are having difficulties finding marriage partners," a KLI researcher said. "This suggests that improving the quality of work for underprivileged groups could also be a way to solve the low birthrate."