RELIABILITY AND ADEQUACY OF FABM-PEICE DATA 
47 
to market or time of harvest. In addition to the many differences 
between the two States from a potato-price standpoint, potato prices 
as reported each month have two or three times the variability or 
dispersion of wheat or cotton prices. There is no world price 
for potatoes in the same sense that there is for wheat and for cot- 
ton, nor is the potato market so well organized. Pius correlation 
coefficients of 0.923 for the pre-war period, 0.988 during the war 
and postwar inflation, and 0.890 for the last few years, indicate 
that, in spite of the many disturbing factors, the tendency is very 
strong for the price of potatoes in the two States to parallel each 
other month by month. It is not nearly so close a relationship 
as that between cotton prices in Southern States, or wheat prices 
FARM AND MARKET PRICES OF COTTON 
1909-1925 
PER 
POUND 
4-0 
|| || | 
— Texas Farm Priee 
35 
, 
/ n i iif-i-ii- o 
¥ 
/\i 
| 
y 
h 
30 
25 
1 fl 
J 
\}\ 
>J|_ 
V \ 
20 
15 
gv 
"f 
rS^ 
S sw 
10 
5 
/ 
Swfv J 
* 
V 
f\ — 
n 
II 
1 M 
1909 
'10 
'II 
1. A. J. O. 
•12 
J. A. J. O. 
'13 
I.A.J. O. 
'14 
J.A.J.O. 
•15 
J.A.J.O. 
'16 
j.A.j.a 
'17 
J.A-J.CL 
'18 
J.A-J.O. 
'19 
AA.J.O- 
'20 
A A. JO. 
•21 
».A.j.a 
•22 
j. a. j. a 
'23 
J.A-J.O. 
'24 
J.A.J.O. 
•25 
j.a.j.0. 
'26 
;.a.j.o.j 
'27 
Fig. 7. — The correlations between the farm prices of cotton in Texas and the average 
prices of middling cotton at New Orleans for the five clays ending the 15th of each 
month are + 0.957 in the pre-war period, from 1910 through 1914 ; + 0.991 from 1915 
through 1919 ; + 0.979 from 1920 through 1925 ; and + 0.989 for the entire period 
from 1910 through 1925 
in Northern States, but it is important nevertheless. Figure 8 
shows the general relationship of the farm-price series in Maine 
and for New York. 
A COMPARISON OF FARM PRICES WITH MARKET PRICES 
It is difficult to obtain series of market prices that are strictly 
comparable with series of farm prices and can therefore be used to 
show their bias. The historical series of farm prices of a product 
in any State would not be closely correlated with a historical series 
of the price of that product at a primary market unless the State had 
been continually either a surplus-producing or a deficit State for the 
entire period for which prices are being compared. There are only 
a few farm products, even in surplus-producing States, which enter 
the regular channels of trade in the same general proportion year 
