For group and world totals denoted in the tables by a t, missing data are imputed based on the relationship of the sum of available data to the total in the year of the previous estimate. The imputation process works forward and backward from 1995. Missing values in 1995 are imputed using one of several proxy variables for which complete data are available in that year. Imputed values are usually not calculated if missing data account for more than one-third of the total in the benchmark year. The variables used as proxies are GNP in U.S. dollars, total population, exports and imports of goods and services in U.S. dollars, and value added in agriculture, industry, manufacturing, and services in US dollars.
Aggregates marked by an s are sums of available data.
Missing values are not imputed. Sums are not computed if more than one-third of the observations in the series or a proxy for the series are missing in a given year. The aggregate ratios are based on available data, including data for economies not shown in the main tables. Missing values are assumed to have the same average value as the available data. No aggregate is calculated if missing data account for more than one-third of the value of weights in the benchmark year.