anchor: Productivity  Business Sector and Major Subsectors, BLS Handbook of Methods (April 1997), pp. 89-98.
positive: pp. 89-98 from the April 1997 BLS Handbook of Methods in Productivity Business Sector and Major Subsectors.
negative: pp. 78-98 of Productivity Business Sector and Major Subsectors, BLS Handbook of Methods (May 1998)