The average age of those who shun interaction with society and hole themselves up inside their homes stands at 26.7, with some 14 percent aged 35 or older, according to a health ministry study released Monday.

According to the nationwide survey of mental health centers and local health offices conducted in March, 20 percent had been physically abusive to a family member.

According to the survey, the centers handled a total of 14,000 social withdrawal cases in 2002.

In contrast, a similar survey conducted by the health ministry in November 2000 that covered the preceding 12-month period showed that such facilities received about 6,100 calls or visits for advice.

Analysis of 3,293 cases in the latest survey in which people visited the centers showed that 76.4 percent of such people were men, according to the Health, Labor and Welfare Ministry.

Experts say that the older such people become, the more difficult it gets for them to reintegrate into society.

In the 2000 survey, only 8.6 percent of the cases involved people aged 36 or older. The results of the latest survey show that in 23.1 percent of the cases, the problem has been ongoing for more than a decade.

Of the cases covered in the survey, 61.4 percent had missed school for long periods.