Birth dates were available for own children of the woman who were present in the home, but, to obtain a complete birth roster, they were estimated (allocated) for children who had died or left home. The birth rosters were derived only for women ever married who were either (1) 14 to 40 years old at the time of the 1960 Census or (2) first married in 1940 or later. The intention was to eliminate women who were so old or had been married so long that most of their children had grown up and left home. However, data for women 35 to 40 years old in 1960 or first married in 1940 to 1944 were purposely included even though it was realized that a considerable proportion of those women would have at least one child absent from home. Women never married were treated childless for purposes of this report, but the data to women ever married include some illegitimate births.

The allocations of birth dates for children absent from home involved several steps. First, the number of absent children was determined by subtraction of the number of the woman's own children present in the home from the number of her children ever born. (In the relatively few cases, amounting to less than one percent, where adoptions or stepchildren caused the number of own children present to exceed the number of children ever born to a woman, data for the oldest children were dropped to make the remaining children present equal to the number of children ever born for purposes of the birth roster.) Second, allocations were made of the positions of the absent children if any, as being born before, between, or after children who were present. Third, an allocation was made of the spacing of each absent child in relation to a prior child or to the date the mother married, and that spacing was added to the date of the prior event to obtain a birth date for the absent child.

The allocations of positions and spacing in the second and third steps cited above were based largely on distributions obtained from the August 1959 Current Population Survey. That survey obtained birth dates (and hence spacing) for both present and absent children ever born to women in a sample of about 35,000 households, and information on whether each child was present or absent. Deceased children were counted as "absent." The allocation tables developed from the 1959 survey for use with the 1960 Census childspacing edits were many and complex, and in some instances were based on few observations. The allocation tables were specific for color and parity of the woman and the interval since marriage or the birth of a previous child. The allocation tables were based on 1959 survey data for women who had at least one child absent from home.

If the tabulations for the present report had been limited to data for women with all their children ever born present in the home, the results would have been somewhat selective of white women, women with few children, and women with recent births or delayed childbearing. Even though the allocations of birth dates for children absent from home were subject to some error, these allocations made a considerable improvement in the quality of the data over what would have been obtained had the data been limited to women with all their children present.

Table A presents a summary of data on the proportion of allocations for children absent from home. Many of the women with children absent had other children who were present so that the proportion of children with allocated birth dates is much less than the proportion of women who had absent children. Thus a woman with two children present and one child absent needed an allocation of birth date for only one-third of her children but she contributed in her entirety to the proportion of women with at least one absent child.

Table A. Proportion of Children Ever Born With Birth Date Allocated, By color and age of Mother, For the United States: 1960

color and age of mother	Mothers ever married with one or more children ever born			Children Ever Born
	Total	With at least one child absent		Total	With birth rate allocated
		Number	Percent of total		Number	Percent of total
White
15 to 19 years	468,904	70,020	14.9	604,477	86,734	14.3
20 to 24 years	2,567,890	234,162	9.1	4,654,035	319,161	6.9
25 to 29 years	3,772,890	347,655	9.2	9,320,430	519,007	5.6
30 to 34 years	4,486,961	506,607	11.3	12,701,477	768,623	6.1
35 to 39 years	4,793,523	991,439	20.7	13,988,828	1,549,832	11.1
Nonwhite
15 to 19 years	89,423	26,149	29.2	140,345	35,557	25.3
20 to 24 years	348,986	89,840	25.7	826,017	147,222	17.8
25 to 29 years	485,764	129,780	26.7	1,558,261	234,919	15.1
30 to 34 years	536,369	162,019	30.2	1,989,573	311,620	15.7
35 to 39 years	511,421	223,904	43.8	1,971,720	447,806	22.7

In the tape files used for tabulation of 1960 Census data, dates of birth and dates of first marriage are coded in terms of the calendar quarter (January-March, April-June, July-September, October-December) and the year. The month and day of the event are not available. The effect of using calendar quarters on the measurement of intervals between events is illustrated by the following example:

Suppose that a group of women married for the first time in July-September 1951 and that each of these women had a first child in October-December 1952. There are 5 calendar quarters in all between the two dates. If the 5 calendar quarters are multiplied by 3 months per quarter, the result is an estimated average spacing of 15 months. The true average spacing depends on how the women and their children are distributed within the two periods. If the women and their children are evenly distributed, then half of the women would have a spacing between marriage and first birth of less than 15.0 months and half of more than 15.0 months. The largest number of combinations of a day in the marriage period with a day in the first-birth period would be associated with a spacing exactly 15.0 months from the marriage day.¹ There would be progressively fewer combinations for successive exact spacings on either side of the peak value of 15.0 months. Half of all possible combinations would fall in a range of 27 days on either side of the median spacing of 15.0 months. The general nature of the distribution is illustrated by the following sketch:


The above example serves several purposes. First, it illustrates the characteristics of the data that are obtained when one date expressed in calendar quarter and year is subtracted from another date expressed in calendar quarter and year. The result is a spacing interval that for a large group of women tends to correspond to the exact average spacing that might be figured from two dates in terms of day, month, and year. In the example, the 15 months is used to mean exactly 15.0 months, not to an interval such as the "15th month." Within the two calendar quarters, the possible combinations of pairs of days are such that there is much concentration on intervals close to 15.0 months and very little chance of extreme errors of as much as 3 months on either side of the 15.0 months midpoint. This concentration means that even if the distribution of a large group of women is moderately- skewed, the difference computed from calendar quarters and years should still come close to representing the average spacing interval for the group. Second, the example provides an indirect justification for showing the average interval between events in terms of months, as given in some tables of this report, where this average was obtained by multiplying the average difference in calendar quarters by 3 months per quarter. Third, the example provides a rationale for a half- and-half apportionment of births by certain kinds of spacing detail discussed in the next section.

In the present report, women born in a specified calendar quarter were tabulated as being at the start of age "n" when they were in the anniversary quarter "n" years later. For example, women born in July-September 1920 were tabulated as being at the start of age 30 in July-September 1950. In tables showing numbers of women of a given parity at the start of a specified year after marriage, the women were tabulated in the manner just described; however, the births of their children were tabulated differently. Half of the births occurring in an anniversary quarter were tabulated as occurring in the woman's age or marriage duration that ended in that quarter and half as occurring in the age or marriage duration that began in that calendar quarter. By way of illustration, half of the first births in April-June 1958 to mothers first married in April-June 1956 were tabulated as occurring in the second year after marriage and half as occurring at the start of the third year after marriage.

In tables showing parity progressions of women, all of which involved women of a given parity at the start of an age or marriage duration, only those births during a year of age or marriage duration were counted which advanced the woman to the next parity. Thus, in the case of a woman who was childless at the start of an age and who had twins during that age, only the first child was counted. The same woman was treated as being of two-parity status at the start of the next age and thus never qualified for Inclusion in a table for women of one parity at the start of an age. Similarly, in tables showing women of given parities at the start of each marriage duration those with children born before marriage were included in the proper parity at the time of their first marriage.
Some tables present data on births cumulated through the midpoint of successive years of age for a birth cohort of women. This procedure yields data similar to information on children ever born to women by single years of age. On the average, women in a single year of age at a survey date are about half way through that age.

In the cumulations of births, one-half of those occurring in calendar quarters in which the mother reached the midpoint of a year of age were tabulated as occurring before the midpoint age and one-half as occurring after the midpoint age.

Some tables show the average number of months between births. These data were obtained by first computing the average number of calendar quarters between births and then by multiplying that average by 3 months per quarter.

Data on cumulated births of each birth order by successive ages or marriage durations of cohorts of women cannot be readily differenced and interpolated in a manner that will yield data comparable to those shown in parity-progression tables.

In tables showing cumulative fertility data, births have been adjusted for the part of a cohort that had not reached the midpoint of a stated age or marriage interval by the time of the 1960 Census. Such data are footnoted in the tables to indicate that they have been adjusted. In order to keep the computer programming reasonably simple, arithmetic proportions, which are approximately correct, were used for the adjustment. These proportions were obtained in the manner Illustrated by the following example:

For women born in the 5-year period from 1925 to 1929, 20 calendar quarters of birth dates were available in the census records-from January-March 1925 to October-December 1929. It was assumed, for the purpose of computing adjustment proportions, that the women were evenly distributed within the 5-year period. Thus, 20 quarters could be taken as representing all possible birthdates from the midpoint of one single year of age to the next single year of age. Of the 20 calendar quarters available, all were sufficiently distant from the 1960 Census date (April 1, 1960) for all women to reach the midpoint of age 30. Each calendar quarter was compared with the April 1, 1960, Census date and given a weight of "1" if it represented attainment of the midpoint of each age, and each was given an appropriate fractional weight if it represented partial experience between the midpoints of one age and the next age. The weights for the 20 calendar quarters were then summed within each desired age interval. For each desired age interval, the adjustment proportion was the ratio of 20 quarters (representing full experience) to the sum of the weights (representing partial experience) for that age interval. The adjustment proportions were applied to uncumulated data on births. Cumulations of births were made after the births were adjusted.

The number of own children living with a woman and the birth dates of those children were determined by a computer examination of the records for every member of the household in which the woman lived. The own children comprise sons and daughters of the woman, excluding insofar as possible for purposes of the present report, any children she has adopted and her stepchildren. Adopted children and stepchildren were partly eliminated from data on own children by a procedure that dropped data for the oldest children when the number of own children present exceeded the number of children ever born to the woman. Less than one percent of the women had more children present than children ever born. A combination of various kinds of evidence ² indicates that roughly 3 percent of the remaining own children are stepchildren and adopted children.

The number of children ever born includes children born to the woman before her present marriage, children no longer living, and children away from home, as well as children borne by the woman who were still living in the home. Although the question on children ever born was asked only of women reported as having been married, the data are not limited to legitimate births.

As explained in the section on "Collection and processing of data," certain records were deleted during the Electronic Processing and tabulation of the child-spacing data. Some of the deleted records represented errors of response or of coding that could not readily be corrected without a further complication of already complex Electronic Processing procedures. The majority of the deletions occurred, however, through minor errors in programming procedures that were discovered too late for repair. Because of the deletions, the numbers of women shown in the present report are smaller than those expected from a full sample and, therefore, are not strictly comparable with those shown In other reports of the 1960 Census. As shown in table B, the shortages amount to about one percent for white women at ages over 24 and to about four percent for nonwhite women of this age range. The shortages are larger for women under age 25 for reasons explained in the section on "Collection and processing of data."

Table B. Estimated Shortage of Women 15 To 39 Years Old In the Present Report Resulting From Processing Errors by age, color, and Year of Birth of Woman, For the United States: 1960
(Based on 5-percent sample)

Subject	White			Nonwhite
	Expected number of women	Tabulated for present report	Percent under-represented	Expected number of women	Tabulated for present report	Percent under-represented
All women
Born in 1940 to 1944	5,725,549	5,200,114	-9.2	809,947	712,629	-12.0
Born in 1935 to 1939	4,810,408	4,662,149	-3.1	689,152	641,526	-6.9
Born in 1930 to 1934	4,847,559	4,791,230	-1.2	705,229	680,480	-3.5
Born in 1925 to 1929	5,402,607	5,333,940	-1.3	727,618	702,892	-3.4
Born in 1920 to 1924	5,719,828	5,691,335	-0.5	703,939	686,156	-2.5
Women ever married with one or more children ever born
15 to 19 years	497,444	468,904	-5.7	98,771	89,423	-9.5
20 to 24 years	2,619,287	2,567,890	-*2.0	366,660	348,986	-4.8
25 to 29 years	3,825,131	3,772,061	-1.4	506,250	485,764	-4.0
30 to 34 years	4,539,755	4,486,961	-1.2	555,747	536,369	-3.5
35 to 39 years	4,843,340	4,793,523	-1.0	526,642	511,421	-2.9

Source: Expected numbers of women derived from 1960 Census of Population, Final report PC(2)-3A, Women by Number of Children Ever Born, tables 2 to 5. Tabulated numbers from tables 19, 20, and 42 of present report.

The effect of the shortages in numbers of women on the birth rates depends on the relative fertility of the women in the deleted records and of the women in the remaining records. At ages under 25, the remaining records were somewhat selective of women ever married with one or more children ever born. This fact can be seen indirectly from table B by comparing the percent underrepresented for all women torn in 1940 to 1944 with the percent underrepresented for approximately the same cohort (i.e., women 15 to 19 years old in 1960) who were ever married and had one or more children ever born; and by comparing data for other cohorts in a similar manner. At ages 15-19 and 20-24, the percent underrepresented is higher for all women than for the mothers ever married, reflecting the effect of relatively fewer deletions for mothers ever married than for other women. At ages 25-29 and above, there is little selective effect.
Table C presents rates of children ever born per 1,000 women, by age, as obtained from tabulations for the present report and as obtained from another report of the 1960 Census. The close agreement of the rates from the two sources of data indicates that the deletions had little effect on rates of children ever born.

Table C. Comparison of Data in the Present Report and Report PC(2)-3a- Children Ever Born Per 1,000 Women 15 To 39 Years Old and Per 1,000 Mothers, By color, And age of Woman, For the United States: 1960
(Based on 5-percent sample)

color and age of mother	All women		Women ever married with one or more children ever born
	Present report	Report PC(2)-3A	Present report	Report PC(2)-3A
White
15 to 19 years	116	117	1,289	1,353
20 to 24 years	998	993	1,812	1,826
25 to 29 years	1,945	1,960	2,471	2,477
30 to 34 years	2,381	2,398	2,831	2,837
35 to 39 years	2,458	2,471	2,918	2,925
Nonwhite
15 to 19 years	197	202	1,569	1,676
20 to 24 years	1,288	1,288	2,367	2,421
25 to 29 years	2,290	2,333	3,208	3,242
30 to 34 years	2,831	2,852	3,709	3,735
35 to 39 years	2,874	2,902	3,855	3,888

Data on childspacing derived from the 1960 Census have a high degree of comparability with data on fertility histories occasionally obtained in the Current Population Survey (CPS). However, the CPS obtains information on the month of birth instead of the calendar quarter, thereby enabling more precise measurements of childspacing intervals than are possible from the 1960 Census data. Also, information on birth dates is obtained in the CPS for children who have died or left home, as well as for children present, whereas birth dates for absent children are estimated for the 1960 Census child- spacing tabulations. Therefore, there is no technical need in the CPS to eliminate from the tabulations women who are so old or have been married so long that many of their children have grown up and left home. The proportion of nonresponses to questions on children ever born and on characteristics of women is smaller in the CPS than in a decennial census. On the other hand, the CPS data on childspacing are based on samples of only 35,000 households (August 1959 CPS) or 50,000 households (June 1965 CPS), and therefore are subject to considerably greater Sampling Variability than the decennial census data. The 1960 Census data in several ways have a wider coverage of persons in group quarters, including inmates of institutions, than the CPS data. This is one reason why the proportion of women ever married tends to be a little higher in the CPS than in a decennial census. Illustrative comparisons of data from the August 1959 CPS with data from the present report are presented in table D.

The usual practice of the Bureau of the Census is to present rates and percentages that are rounded upward in the last digit shown if the next digit would be 5 or more. However, the tabulation program used for the present report in many instances presents rates and percentages that are not rounded up.

Table D. Percent Ever Married And Number Of Children Ever Born Per 1,000 Women By Successive ages Of Women For White Women Born In 1925 To 1929, For The United States: 1960 Census And August 1959 Current Population Survey (Data tallied to midpoint of successive ages. Census data based on 5-percent sample. Current Population Survey (CPS) data based on sample of about 35,000 households)

age	Percent ever married		Children Ever Born per 1,000 women
	Census	CPS	Census	CPS
15 years	2.1	1.9	8	5
16 years	5.3	5.1	22	16
17 years	11.1	10.5	50	40
18 years	20.7	20.4	103	94
19 years	32.9	33.5	193	175
20 years	45.6	46.2	322	300
21 years	57.5	57.8	483	468
22 years	67.1	68.1	662	638
23 years	73.9	76.5	849	838
24 years	78.8	82.0	1,041	1,042
25 years	82.4	86.0	1,235	1,258
26 years	85.0	88.4	1,424	1,477
27 years	86.9	90.0	1,606	1,667
28 years	88.4	91.1	1,778	1,853
29 years	89.6	92.3	1,936	2,035
30 years	90.5	193.2	2,082	12,192

¹Data adjusted for the part of the cohort that has not attained the midpoint of the stated age.

Source: Census data from table 19 of this report. CPS data from Current Population Reports, Series P-20, No. 108, "Marriage, Fertility, and Childspacing: August 1959," tables 5 and 7.

In tables presenting cumulated births adjusted for the part of a cohort that has not reached an age or marriage duration, certain group totals were independently adjusted, with the result that data by some characteristics, e.g., detailed marital status, add to a total that differs slightly from the independently adjusted group total.