A STATISTICAL METHOD FOR MEASURING “MARGINAL UTILITY’ 191
Similarly, multiplying (11) and (4) we obtain
SspsW ee p2/p1 (13)
SioiW1 ¢o/
Before we can plot the want curve for food we need to get ¢3
from the budget tables; and before we can do the same for rent
we need similarly to find p;.
Suppose we find ¢5=30% and p;=24% ; we now have all the
data needed for calculating and plotting the two want curves
(for food and shelter). All our data may be tabulated for refer-
ence as follows:
Si = $1000 per year
¢ 1
Fr
*. 4
W
J wan
1 ¢*]
er
per
IS
S; = $600 per year
$2 = .50
n2 20
: it per “Ib.”
1 per “sq. {i
1 wantab
Wa=
S; = $1440 per year
bs = .30
Ps = 2D
Vy 81.33% per “lb.”
KR: $3 per “sq. ft.”
Ws: = .33% wantabs
In this table the four given magnitudes are S,, Fs, Rs, Wo, all in
the middle column and three of them being the units of measure-
ment assumed.
The remaining magnitudes are all calculated from these four,
or obtained from budget tables or from our assumed conditions.
We could now easily plot the quantity of food and its want-
ability from
Sign 1000 X .40
Ww. 75 Z $1.331 = 1.00
these two being the “latitude and longitude” of one point (that
for Case 1) ; and, likewise plot the analagous quantity and want-
ability for Case 3:
n
Sade _ 144030 _ 394.00
Wal «1.331 = 44.
Such a curve would be none other than the “curve of diminishing
utility of food” used in our text books but not hitherto reducible
to statistics.
The figures show that (according to our purely illustrative
data) if the quantity (or, more strictly, index) of food consumed
is increased from 300 to 324 the want-for-one-more unit of it
decreases from 1.00 to .44 wantabs.