The figures from the 25-percent sample tabulations are subject to Sampling Variability, which can be estimated roughly from the standard errors shown in tables B and C. These tables
^{2} do not reflect the effect of response variance, processing variance, or bias arising in the collection, processing, and estimation steps. Estimates of the magnitude of some of these factors in the total error are being evaluated and will be published at a later date. The chances are about two out of three that the difference due to Sampling Variability between an estimate and the figure that would have been obtained from a complete count of the population is less than the standard error. The chances are about 19 out of 20 that the difference is less than twice the standard error and about 99 out of 100 that it is less than 2£ times the standard error, The amount by which the estimated standard error must be multiplied to obtain other odds deemed more appropriate can be found in most statistical text books.
Table B shows standard errors of estimated numbers up to 50,000. The relative sampling errors of larger estimated numbers are somewhat smaller than for 50,000. For estimated numbers above 50,000, however, the nonsampling errors, e.g., response errors and processing errors may have an increasingly important effect on the total error. Table C shows rough standard errors of data in the form of percentages. Linear interpolation in tables B and C will provide approximate results that are satisfactory for most purposes.
Table B. Rough Approximation to Standard Error of Estimated Number
(Range of 2 chances out of 3)
Estimated number |
Standard error |
50 |
15 |
100 |
20 |
250 |
30 |
500 |
40 |
1,000 |
50 |
2,500 |
80 |
5,000 |
110 |
10,000 |
160 |
15,000 |
190 |
25,000 |
250 |
50,000 |
350 |
Table C. Rough Approximation to Standard Error of Estimated Percentage
(Range of 2 changes out of 3)
Estimated percentage |
Base of percentage |
500 |
1,000 |
2,500 |
10,000 |
25,000 |
100,000 |
2 or 98 |
1.3 |
0.9 |
0.5 |
0.3 |
0.1 |
0.1 |
5 or 95 |
2.0 |
1.4 |
0.9 |
0.4 |
0.2 |
0.1 |
10 or 90 |
2.8 |
2.0 |
1.2 |
0.6 |
0.3 |
0.2 |
25 or 75 |
3.8 |
2.7 |
1.5 |
0.7 |
0.4 |
0.2 |
50 |
4.4 |
3.1 |
1.6 |
0.8 |
0.5 |
0.3 |
For a discussion of the Sampling Variability of medians and means and of the method for obtaining standard errors of differences between two estimates, see 1960 Census of Population, Volume I, Characteristics of the Population, Part 1, United States Summary.
Illustration: In table 6 the income class under $1,000 in Alabama shows 4,727 husband-wife families containing other relatives and having a head or wife 65 years old or over. Table B shows that for an estimate of 4,727 the approximate standard error is 107, which means that the chances are approximately 2 out of 3 that the results of a complete census "would not differ by more than 107 from this estimated 4,727. It also follows that there is only about 1 chance in 100 that a complete census result would differ by as much as 268, that is, by about 2 ½ times the number estimated from table B.