sentences:  For this reason, the term translog index is sometimes used for a Törnqvist index.The Törnqvist index is approximately "consistent in aggregation", meaning that the almost exactly the same index values result from (a) combining many prices and quantities together, or (b) combining subgroups of them together then combining those indexes.For some purposes (like large annual aggregates), this is treated as consistent enough, and for others (like monthly price changes) it is not.