RELIABILITY AND ADEQUACY OF FARM-PRICE DATA 
41 
prices in Northern States is really very small as compared with the 
variability of prices of livestock. In the more important butter 
States the sample is sufficiently large to make the probable error so 
small that four times the relative probable error is only about 2.5 per 
cent, nearly as low as for wheat, cotton, and hog prices in important 
producing States. 
Table 21. — Farm prices of butter and butterfat; Selected illustrations of size 
of sample, measures of dispersion, and probable errors 
[Per pound] 
Product, State, and date 
Number 
of 
reports 
Average 
price 
(arith- 
metic 
mean) 
Standard 
devia- 
tion of 
reports 
Coeffi- 
cient of 
varia- 
bility 
Probable 
error 
of the 
average 
price or 
mean 
Relative 
probable 
error 
Four 
times 
relative 
probable 
error l 
Minnesota, April, 1925: 
Butter... . .- 
126 
111 
80 
15 
80 
40 
12 
17 
34 
Cents 
42.1 
42.8 
34.2 
41.6 
42.9 
44.5 
44.6 
44.5 
45.9 
Cents 
3.9 
3.9 
8.6 
3.1 
3.4 
3.7 
4.9 
4.9 
7.6 
Per cent 
9.2 
9.1 
25.1 
7.5 
7.9 
8.4 
11.1 
11.0 
16.6 
Cents 
0.23 
.25 
.65 
.56 
.26 
.40 
.96 
.80 
.90 
Per cent 
0.5 
.6 
1.9 
1.3 
.6 
.9 
2.2 
1.8 
1.9 
Per cent 
2.0 
Butterfat 
2.4 
Alabama, April, 1925: 
7.6 
5.2 
Wisconsin, June, 1925: 
Butter . 
2.4 
3.6 
California. April, 1925: 
Butter 
8.8 
Butterfat - 
7.2 
Maryland, March, 1926: 
Butter -. 
7.6 
i The probabilities are ninety-nine out of one hundred that the average of a much larger sample col- 
lected in the same way and at the same time would not vary from this average by more than four times 
the probable error. 
The price of butterfat has been obtained only since October, 1920. 
For the United States as a whole the prices of butter and butterfat 
are usually about the same in the summer months, but butterfat 
prices are somewhat higher during the winter months than butter 
prices. Farm prices of butter during the postwar years show a 
greater increase over prices during pre-war years than do the pri- 
mary-market price of 92-score butter. The quantity of country- 
made butter has steadily decreased during the period, as creamery 
butter has increased, and the quality has materially improved. A 
much larger proportion of farm butter is sold at the retail price 
level than was the case 10 or 15 years ago. 
EGGS AND CHICKENS 
There is probably no one farm product that is more generally sold 
throughout the country than eggs. Usually more reports are received 
on egg prices than on almost any other farm product. Table 22 de- 
scribes the egg-price samples from a number of States in different 
parts of the country. Because of the wide seasonal differences in the 
prices of eggs, prices in a summer month and those 'in a winter 
month in several of the States are shown for comparison. 
