Japan's labor ministry says an improper method for surveying wages and working hours at private-sector companies was included in a manual used in 2004.
The monthly surveys were supposed to cover all large businesses with 500 or more workers. But the ministry was found to have covered only about one third of such firms in Tokyo since 2004.
Japan's labor minister has pledged to find out why his ministry kept releasing improper job statistics that apparently led to underpayment of benefits to millions of people.
At a news conference on Friday, Takumi Nemoto offered deep apologies for causing trouble to the public over the ministry's release of statistics compiled through improper methods for years. The data in question cover corporate salaries and working hours surveyed monthly.