This is Matched Pair 1 + 2 in the new series of 4
I won´t try to explain the paintings.
But for the fun of it I will let McGraw-Hill Science and Technology come with there definition of Matched Pairs.
Matched Pairs :
The design of an experiment for paired comparison in which the assignment of subjects to treatment or control is not completely at random, but the randomization is restricted to occur separately within each pair.
More art by Cay HERE
Traveling girl. photo by HERMES