Nikkei JGB Index is average yield index at market calculated using interest rate, redemption date, traded price of 10-year JGB. It has been calculated daily since October 1995 and appeared in morning edition of The Nikkei. Other than Nikkei JGB Index, 3 sub indices are available; long-term (matured equal to or more than 7 years), medium-term (matured equal to or more than 3 years - less than 7 years), and short-term (matured less than 3 years).
Price using for index calculation
Until November 1998: TSE listing price
From December 1998 to July 2002: OTC Standard Bond Quotations announced by JSDA
From August 2002: Reference Statistical Prices [Yields] for OTC Bond Transactions announced by JSDA
From June 2017: Start using negative yield JGB prices (retroactively re-calculate since December 2nd, 2014)