For the forthcoming comprehensive revision, the calculation of implicit price deflators (IPD's) will change. IPD's are weighted averages of the most detailed price indexes used in estimating real output, and the currently published IPD's are calculated as the ratio of current- to constant-dollar output multiplied by 100. The new IPD's will be calculated as the ratio of current- to chained-dollar output multiplied by 100. For all but the most recent estimates, the new IPD's will be identical to the chain-type price indexes because the weights used to aggregate the detailed prices for the two measures will be the same.

For the revised estimates beginning with the third quarter of 1994, the weights used for the chain-type output and price measures will be those for 1994 because weights for 1995 are not available./1/ Thus, the weights used for the chain-type price indexes for each period will be fixed 1994 weights, and those used for the IPD's will be the chained-dollar weights for each period.

In addition to differences between the IPD's and the chain-type price indexes for the most recent periods, there also will be small differences for earlier quarters because the quarterly chain-type output and price indexes are based on annual weights and because both quarterly indexes are independently adjusted for consistency to the corresponding annual indexes.

1. The estimates for the year 1995 to be released in January 1996 also will be based on 1994 weights. Weights for 1995 will be incorporated during the annual NIPA revision currently scheduled for release in July 1996. (For a more detailed discussion of the weights used for current periods, see Allan H. Young, "Alternative Measures of Change in Real Output and Prices, Quarterly Estimates for 1959–92" in the March 1993 SURVEY.)