 A unit comparison: The ratio of [individual \(i\)’s welfare gain or loss if we switch from alternative \(y_1\) to alternative \(x_1\)] to [individual \(j\)’s welfare gain or loss if we switch from alternative \(y_2\) to alternative \(x_2\)] is \(\lambda\), where \(\lambda\) is some real number, formally \(((W_i (x_1) - W_i (y_1)) / (W_j (x_2) - W_j (y_2)) = \lambda\). (Again, the comparison is intrapersonal if \(i = j\), and interpersonal if \(i \ne j\).)