For persons in housing units at the time of the 1960 Census, the sampling unit was the housing unit and all its occupants; for persons in group quarters, it was the person. On the first visit to an address, the enumerator assigned a sample key letter (A, B, C, or D) to each housing unit sequentially in the order in which he first visited the units, whether or not he completed an interview. Each enumerator was given a random key letter to start his assignment, and the order of canvassing was indicated in advance, although these instructions allowed some latitude in the order of visiting addresses. Each housing unit to which the key letter "A" was assigned was designated as a sample unit, and all persons enumerated in the unit were included in the sample. In every group quarters, the sample consisted of every fourth person in the order listed. The 1960 statistics in this report are based on a subsample of one-fifth of the original 2 1/2-percent sample schedules. The subsample was selected on the computer, using a stratified systematic Sample Design. The strata were made up as follows: For persons in regular housing units there were 36 strata, i.e., 9 household size groups by 2 tenure groups by 2 color groups; for persons in group quarters, there were 2 strata, i.e., the 2 color groups.

Although the sampling procedure did not automatically insure an exact 5-percent sample of persons, the Sample Design was unbiased. Generally, for large areas, the deviation from the estimated sample size was found to be quite small. Biases may have arisen, however, when the enumerator failed to follow his listing and sampling instructions exactly during the designation of the 25-percent sample.

The statistics based on the 5-percent sample of the 1960 Census returns are estimates that have been developed through the use of a Ratio Estimation procedure. This procedure was carried out for each of the following 44 groups of persons in each of the sample weighting areas:³

Group	Sex, color, and age	Relationship and tenure
	Male white:
1	Under 5
2	5 to 13
3	14 to 24	Head of owner household
4	14 to 24	Head of renter household
5	14 to 24	Not head of household
6-8	25 to 44	Same groups as age group 14 to 24
9-11	45 and over	Same groups as age group 14 to 24
	Male nonwhite:
12-22	Same groups as male white
	Female white:
23-33	Same groups as male white
	Female nonwhite:
34-44	Same groups as male white

The sample weighting areas were defined as those areas within a State consisting of central cities of Urbanized Areas, the remaining portion of Urbanized Areas not in central cities, urban places not in Urbanized Areas, and rural areas.⁴

For each of the 44 groups, the ratio of the complete count to the sample count of the population in the group was determined. Each specific sample person in the group was assigned an integral weight so that the sum of the weights would equal the complete count for the group. For example, if the ratio for a group was 20.1, one-tenth of the persons (selected at random) within the group were assigned a weight of 21, and the remaining nine-tenths a weight of 20. The use of such a combination of integral weights rather than a single fractional weight was adopted to avoid the complications involved in rounding in the final tables. In order to control a potential bias in the estimates, where there were fewer than 275 persons in the complete count in a group, or where the resulting weight over 80, groups were combined in a specific order to satisfy both of these two conditions.

These ratio estimates reduce the component of sampling error arising from the variation in the size of household and achieve some of the gains of stratification in the selection of the sample, with the strata being the groups for which separate ratio estimates are computed. The net effect is a reduction in the sampling error of most statistics below what would be obtained by weighting the results of the 5-percent sample by a uniform factor of twenty. The reduction in sampling error will be trivial for some items and substantial for others. A byproduct of this estimation procedure, in General, is that estimates for this sample are generally consistent with the complete count with respect to the total population and for the subdivisions used as groups in the estimation procedure.

The figures from the 5-percent sample tabulations are subject to Sampling Variability, which can be estimated roughly from the standard errors shown in tables B, C, D, and E.

These tables 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 are being published in reports in Series ER 60, Evaluation and Research Program of the U.S. Censuses of Population and Housing: 1960. 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 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 textbooks.

Table B, shows rough standard errors of estimated numbers up to 500,000 for household and population characteristics. For estimated numbers above 500,000, however, the nonsampling errors, e.g., response errors and processing errors, may have an increasingly important effect on the total error. Tables C and D contain rough standard errors of data in the form of percentages. Standard errors of estimated percentages for household characteristics are shown in table C, and those for population characteristics are presented in table D. Table E gives standard errors of estimated numbers of children ever born per 1,000 women ever married. Linear interpolation in tables B, C, D, and E will provide approximate results that are satisfactory for most purposes.

Illustration: Table 1 shows that there were an estimated 463,513 males with socioeconomic status score 80 to 89 between the ages of 55 to 64 years old in the United States in 1960. Table B shows that for an estimated 463,513 persons, the approximate standard error is 3,900. This means that the chances are approximately two out of three that the results of a complete count would not differ by more than 3,900 from a sample estimate. It also follows that there is only about 1 chance in 100 that the results of a complete count would differ by as much as 9,750; that is, by about 2 ½ times the standard error.

Table B. Approximate Standard Errors of Estimated Totals for Household Characteristics and Population Characteristics
(Range of 2 chances out of 3)

Size of estimate	Standard error for--
	Household characteristics	Population characteristics
1,000	100	100
2,500	200	200
5,000	300	400
10,000	400	600
25,000	600	900
50,000	900	1,700
100,000	1,300	2,400
250,000	2,000	3,800
500,000	2,700	5,400

Table C. Approximate Standard Error of Estimated Percentage for Household Characteristics
(Range of 2 chances out of 3)

Estimated percentage	Size of base of percentage (thousands)
	10	25	100	250	500	1,000
2 or 98	0.8	0.3	0.2	0.1	0.1	0.1
5 or 95	1.0	0.5	0.3	0.2	0.1	0.1
10 or 90	1.5	0.8	0.4	0.2	0.2	0.1
20 or 80	1.7	1.0	0.5	0.3	0.2	0.2
35 or 65	1.9	1.2	0.6	0.4	0.3	0.2
50	2.0	1.3	0.6	0.4	0.3	0.2

Table D. Approximate Standard Error of Estimated Percentage for Population Characteristics
(Range of 2 chances out of 3)

Estimated percentage	Size of base of percentage (thousands)
	10	25	100	250	500	1,000
2 or 98	1.1	0.6	0.3	0.2	0.2	0.1
5 or 95	1.6	0.9	0.5	0.3	0.2	0.2
10 or 90	2.2	1.4	0.7	0.5	0.3	0.2
20 or 80	3.0	2.0	1.0	0.6	0.4	0.3
35 or 65	3.4	2.2	1.1	0.7	0.5	0.4
50	3.7	2.4	1.2	0.8	0.5	0.4

Table E. Approximate Standard Error of Estimated Number of Children Ever Born per 1,000 Women Ever Married
(Range of 2 chances out of 3)

Estimated number of women ever married	Standard error if the number of children ever born per 1,000 women ever married
	500	1,000	2,000	3,000	4,000	4,500
2,500	55	90	150	210	260	280
10,000	25	45	75	100	130	140
25,000	20	30	50	70	80	90
50,000	15	25	40	60	80	90
100,000	10	15	30	45	60	65
250,000	10	10	20	30	40	40
500,000	5	10	15	20	25	30
1,000,000	5	5	10	15	20	20