# What are indices in Economics?

Really, what are indexes in Economics? And bilateral and multilateral indexes?

Take the Malmquist Index: it is a bilateral index, even though it uses four numbers: $$Q_1$$, $$Q_2$$, $$Q_3$$ and $$Q_4$$?

And superlative index numbers?!

• Indices (the correct plural) aggregate high dimensional data to a single number. So they are basically functions from high dimensional spaces to one dimension. Feb 11 '21 at 8:49
• Actually: grammarist.com/usage/indexes-indices. But why is the Malmquist Index a bilateral index if it maps a four-dim space to a 1-dim one? Feb 11 '21 at 12:19
• It is bilateral because the number refers to something happening between two countries. Feb 11 '21 at 12:21
• So the bilateral relates to the numerator and denominator then? Feb 11 '21 at 12:25
• It is an index for a bilateral relationship. In general, that need not be related to any fraction. Feb 11 '21 at 12:30