Concept:The circular test in index numbers checks if the product of chain indices over a cycle equals 1.Explanation:The condition Pab×Pbc×Pca=1 means that when you go from period a to b, then b to c, and finally c back to a, the overall index should return to the starting value (1).This property is known as the circular test.It is an extension of the time reversal test and factor reversal test, but specifically requires consistency in a closed loop of three or more periods.Answer:Circular Test