Measure how the quantity demanded of one good responds to a price change of another, classifying them as substitutes or complements.
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Cross-price elasticity | Exy = (ΔQx/Qx) / (ΔPy/Py); positive = substitutes, negative = complements | Marshallian demand / Hicks, Value and Capital (1939) |