In economics, the Törnqvist index is a price or quantity index. In practice, Törnqvist index values are calculated for consecutive periods, then these are strung together, or 'chained'. Thus, the core calculation does not refer to a single base year. In economics, the Törnqvist index is a price or quantity index. In practice, Törnqvist index values are calculated for consecutive periods, then these are strung together, or 'chained'. Thus, the core calculation does not refer to a single base year.