A STATISTICAL METHOD FOR MEASURING “MARGINAL UTILITY” 181
reach adjustment or equilibrium) will also have the same want-
for-one-more unit of housing.
This intercomparability is more truly applicable as between
large groups of workingmen’s families, as revealed in the average
family budgets, than as between two particular families.
In fact, while it helped at the outset to picture three identical
families, just as it helped to think of our measurements as in
“pounds” or “square feet,” in practice—at least in the present
state of our knowledge and statistics—we can scarcely expect
to measure the wants of any individual family. Variability and
chance enter in too much. To make any progress toward prac-
tical measurements we must combine hundreds of families, and
use only averages—albeit the “average family” is as mythical
and non-existent, except as an average, as is the “economic man.”
In this way we may hope to reach at least an approximate
measure of man’s economic psychology in the mass.
There is one field in which, without any guidance but common
sense, we have expressed in figures the appraisal of mankind of
the comparative value of money to people of different incomes.
That field is taxation. Not only would it seem to all reasonable
people unfair to assess the same number of dollars of taxes against
the workingman as against the millionaire but to most people it
would seem unfair to assess even the same rate per dollar of
income. Even the philosophic doubter, if himself taxed unfairly,
would be apt to know it! He would scarcely be satisfied if told
that any comparison between his tax burden and others is mean-
ingless because his mental phenomena and others’ are incom-
mensurable.
At any rate, whether justified or not, the method here set, forth
does proceed on the assumption of commensurability, and my
object in setting this forth is not so much to prove it correct as
frankly to face it and point it out, as an assumption.
Summary of Assumptions
The following is a complete summary of the assumptions under-
lying the second pair of equations, those on wantability.
(a) Adjustment. The ‘budget groups used, like food, are
assumed to be sufficiently subject to graduation in quantity and
quality; and to be, in other ways, sufficiently adjustable, and
adjusted, that the marginal dollar of an average or typical famaly