RELIABILITY AXD ADEQUACY OF FARM-PRICE DATA 29 
Maryland was practically self-sufficing so far as the 1925 corn 
crop was concerned; in fact, corn was shipped from Maryland to 
both Virginia and Pennsylvania. The 15th-of -the-month ' price re- 
flects this situation better than the December 1 price. The December 
I price had a coefficient of variability of 22 per cent when the few 
high prices from parts of the State where very little corn is raised 
were included, whereas the 15-of-the-month prices which were from 
sections of the State where some corn was being sold, showed only 
II per cent variability. 
The relative probable errors of these samples indicate that the 
probabilities are ninety-nine out of one hundred that an indefinitely 
larger sample collected in the same way and at the same time would 
not vary more than about 2 per cent for Iowa, 7 or 8 per cent for 
Georgia and Pennsylvania, and 5 per cent for Maryland from the 
averages obtained from these samples. For a State of surplus pro- 
duction like Iowa, the sample is large enough, considering the small 
variability of the sample, to give a high degree of stability to the 
average. For Maryland the greater variability of the December 1 
prices as compared with those for the 15th of the month is offset by 
the larger sample; and as a result, the relative probable error in 
both cases is about 1.3 per cent, and four times the probable error 
would be only 5 per cent even in this relatively small State where 
agricultural conditions vary greatly. Both Georgia and Pennsyl- 
vania are deficit States. The variability is fairly high and the num- 
ber of reports not large, and as a result the average obtained is much 
less stable than in a surplus corn State. The December 1 prices for 
Iowa have less than half the variability of the prices in the North 
Dakota sample. North Dakota has both surplus and deficit areas of 
corn production and a wide range in the quality of corn produced. 
The variability of the corn prices in a surplus corn State such as Iowa 
is about the same as that of wheat prices in a surplus wheat State. 
Both Kansas and Iowa are large States from which a good-sized 
sample of prices can be obtained each month. Low variability and 
large samples result in average prices that are highly stable and re- 
liable. Prices of wheat even in States that produce little wheat are 
dominated by the market prices prevailing in the central markets, and 
this fact tends to hold the variability of wheat prices lower than the 
variability of prices of corn which is largely fed on the farm where 
produced or sold to a neighbor. 
Oats are sold in the organized markets of the country, but they 
are like corn in that much of the crop is fed in the neighborhood 
where it is grown, except in the large surplus-producing oat States 
of the Middle -West. Table 11 shows that the coefficient of varia- 
bility of oat prices is seldom below 10 per cent, even in the surplus- 
producing oat States of North Dakota, Illinois, and Indiana. Only 
in one of the Southern States does the variability rise much above 
15 per cent. In North Dakota the coefficient of variability was re- 
duced from 15.3 to 6.1 per cent by eliminating a few high prices 
which were probably for especially selected seed oats. Quotations 
of seed prices undoubtedly occur with greater frequency among oat 
prices than among wheat or corn prices. A large part of the wheat 
