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The rise of cohabitation in the United States: New historical estimates

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The Rise of Cohabitation in the United States: New Historical Estimates
Catherine Fitch, Ron Goeken and Steven Ruggles
1
Minnesota Population Center
University of Minnesota
March 2005
Prepared for presentation at the annual meeting of the Population Association of America,
Philadelphia, March 31-April 2 2005.
1
Contact Catherine Fitch at fitch@pop.umn.edu.
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The rise of cohabitation in the United States in the late twentieth century is an important
component of the dramatic changes in marriage, family formation and childbearing (e.g.,
Bumpass, Sweet and Cherlin 1991; Bumpass and Lu 2000; Casper and Bianchi 2002; Manning
1995). This increase, first noted in the 1970s, was initially inferred from household composition
because few data sources collected direct information on couples “living together” (Glick and
Norton 1977, Glick and Spanier 1980). Research on cohabitation exploded in the 1980s as the
trend accelerated and when longitudinal data sources, such as the National Survey of Families
and Households, provided nationally representative datasets designed for studying cohabitation.
Despite a wealth of new information on cohabitating couples—including the implications
of cohabitation on family formation, relationship stability, childbearing and child well-being—
there are few estimates of cohabitation that assess the dramatic change over time (e.g., Bumpass
and Sweet 1989, Bumpass and Lu 2000). Studies that examine cross-sectional differentials, such
as race, educational attainment and place of residence, are even rarer.
This paper improves on previous attempts to infer cohabitation from the decennial
census. The 1990 and 2000 censuses included specific responses for “unmarried partner” in the
relationship question; previous censuses classified these individuals in broader
“partner/roommate” or “partner/friend” categories. Our goal is to infer as best we can which
individuals in the censuses of 1960 though 1980 would have described themselves as opposite-
sex unmarried partners if that option had been available on the census. We do this by first
developing rules to identify households that are likely contain an unmarried partner, and then by
applying a regression model to refine these measures.
2
POSSLQ and Adjusted POSSLQ
The acronym POSSLQ—“Persons (or Partners) of Opposite Sex Sharing Living
Quarters”—was coined by Census Bureau staff in the late 1970s. POSSLQ households—termed
“Unmarried Couple Households” by the Census Bureau—are composed of two unrelated adults
of the opposite sex (one of whom is the householder) who share a housing unit with or without
the presence of children under 15 years old. According to this definition, unmarried couple
households may contain only two adults (Casper and Cohen 2000). Scholars use POSSLQ (or
unmarried couple) households to estimate the number of cohabiting couples. The number of
unmarried couple households from the decennial censuses of 1960 to 1980 serves as one of the
few measures of cohabitation in that period (e.g., Smock and Manning 2004).
These widely-cited census statistics on the number of POSSLQ households are flawed.
The numbers cited for 1960 and 1970 derive from the census volumes on “Persons by Family
Characteristics” (U.S. Census Bureau 1964: Table 15; 1973: Table 11), and refer not to
unmarried-couple households but to the total number of persons residing with primary
individuals of the opposite sex.
2
This measure misses many actual POSSLQ households because
it does not allow for the presence of children of the household head who are under 15 years old.
Much more problematic, however, the measure is not a count of couples, but rather of all
individuals residing with a head of the opposite sex. Thus, for example, a household containing
an elderly female head with four male lodgers has been interpreted as four separate POSSLQ
households. These errors are easily corrected using census microdata, and the corrections have a
significant impact on the trend over time.
2
Primary individuals are persons residing in households with no family members and with or without non-family
members.
3
Figure 1 compares the published unmarried-couple statistics (U.S. Census Bureau 2004)
with new estimates from the Integrated Public Use Microdata Series (IPUMS) (Ruggles et al.
2004). The published numbers for 1960 and 1970 are significantly overstated compared with the
IPUMS estimates, and those for 1980, 1990 and 2000 are slightly understated. The latter
discrepancy probably arises from a difference in the source; the IPUMS numbers are tabulated
from the decennial census and the published numbers for 1970 through 2000 come from the
Current Population Survey. Using a consistent measure with a consistent source suggests that the
increase in cohabitation between 1960 and 2000 was more than 60% greater than previously
recognized.
Figure 1. Comparison of published and tabulated estimates
of unmarried couple (POSSLQ) households
0
1,000
2,000
3,000
4,000
5,000
6,000
1960 1970 1980 1990 2000
Census year
Number of couples (000s)
Published statistics
Tabulated from IPUMS
4
Several authors have suggested refinements of the POSSLQ measure (Chevan 1966;
Hatch 1995; Moffit, Reville, and Winkler 1998). The most influential of these changes was
implemented by Casper and Cohen (2000), who broadened the definition to allow other adults in
the household. In particular, Casper and Cohen’s “Adjusted POSSLQ” measure permits any
number of adults related to the householder and any adult children in unrelated subfamilies.
Casper and Cohen correctly noted that the traditional measure excludes cohabitors who have
children aged 15 or older, and the adjustment was designed to capture these cases. Table 1
compares the rules for POSSLQ and Adjusted POSSLQ.
Table 1. Rules for designating POSSLQ households
POSSLQ
a. Household must have a householder aged 15+
b. Household must include one other person aged 15+ who is unrelated and of the opposite sex as
the householder
c. Household cannot include any other persons aged 15+
ADJUSTED POSSLQ (Casper and Cohen 2000)
a. Household must have a householder aged 15+
b. Household must include one other person aged 15+ who is unrelated, not a foster child, and of
the opposite sex as the householder
c. Household cannot include any other persons aged 15+, except for relatives of the reference
person and persons listed as a child in an unrelated subfamily
Figure 2 compares POSSLQ and Adjusted POSSLQ for the period 1960 to 1980 and
compares both POSSLQ measures with opposite sex “Unmarried Partners” in 1990 and 2000.
3
The relationship to householder question on the census forms in 1990 and 2000 included an
explicit category for unmarried partners (see Figure 3), instead of the vaguer categories of
3
The census, unlike the Current Population Survey (CPS) did not classify unrelated subfamilies after 1960. To
implement Adjusted POSSLQ in the census, we therefore inferred unrelated subfamily status from the IPUMS
family interrelationship variables (Ruggles 1995). Since the CPS subfamily variables are problematic, this
implementation of Adjusted POSSLQ is probably more accurate than the CPS-based version (Ruggles and Brower
2003).
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partner, friend, or roommate that were enumerated in previous census years. As shown in Figure
2, the Adjusted POSSLQ measure yields substantially higher estimates than either POSSLQ or
unmarried partners in all census years.
Figure 2. Comparison of number of cohabiting households according to POSSLQ,
Adjusted POSSLQ, and Unmarried Partner measures
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
1960 1970 1980 1990 2000
Census year
Number of couples (000s)
POSSLQ
Adjusted POSSLQ
Umarried Partner
Both the POSSLQ and the Adjusted POSSLQ measures capture many persons who were
not actually cohabiting, especially in the earlier census years. Between 30 and 40 percent of
households identified by these measures in 1990 and 2000 do not include an unmarried partner.
Moreover, when we examine individual census records in earlier census years, most of the cases
do not look like cohabiting couples. Table 2 shows some typical examples, drawn from the
beginning of the 1960 census sample. Most of the POSSLQ households in this period appear to
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be typical boarding or domestic service arrangements, and we have little reason to suspect that
they were actually cohabitors.
Figure 3. Census 2000 inquiry on relationship to householder
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Table 2. Examples of POSSLQ households in 1960
Relationship Age Sex Race Marital Status
Head 51 Female White Widowed
Child 11 Male White Never married
Boarder 32 Male White Divorced
Head 30 Female White Married, spouse absent
Child 12 Female White Never married
Child 11 Female White Never married
Child 1 Female White Never married
Boarder 42 Male White Widowed
Head 44 Male Black Widowed
Child 13 Female Black Never married
Child 12 Female Black Never married
Child 11 Male Black Never married
Child 8 Male Black Never married
Child 8 Female Black Never married
Child 7 Female Black Never married
Child 5 Female Black Never married
Child 3 Female Black Never married
Child 3 Male Black Never married
Employee 53 Female Black Widowed
Head 45 Female White Divorced
Employee 46 Male Black Separated
Potential Unmarried Partners
Our goal is to infer unmarried partner status in census years before it was a specific
census category. We do not attempt to uncover cohabitation that would not have been revealed
by the census in 1990 or 2000. In essence, we seek to estimate how many people acknowledged
cohabitation in each census; thus, we focus on self-identified cohabitation. Self-identified
cohabitation is analogous to the census concept of self-identified race. Like racial categories,
categories of relationships between couples, such as cohabitation and marriage, are socially
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constructed. Just as the race question does not attempt to measure genetic heritage, we do not
attempt to estimate the number of legally unmarried coresident persons with a sexual
relationship. Clearly, estimation of sexual relations is impossible with census data for any period;
acknowledged cohabitation is the salient measure for study of historical change in living
arrangements.
Other sources, such as the National Survey of Households and Families (NSFH) and
National Survey of Family Growth (NSFG), ask multiple questions on cohabitation and uncover
higher numbers of cohabitors than are self-identified in the census (Casper and Cohen 2000).
Some of this difference may occur because cohabitors intentionally or unintentionally fail to
identify themselves as unmarried partners in the census. In other cases, people may cohabit
informally but still maintain two residences, and so are not enumerated in the same household by
the census. In the NSFH, for example, persons are counted as cohabitors if they “stay in the
household half the time or more,” regardless whether or not they also have a separate household.
Moreover, the census only identifies persons who are partners of a householder, whereas surveys
can identify persons cohabiting with other household members; the NSFH data suggest that the
census thereby misses about 3 percent of cohabitors (Casper and Cohen 2000).
Both POSSLQ and Adjusted POSSLQ identify many households without unmarried
partners, and exclude many households that do have an unmarried partner. To better identify
households likely to include an unmarried partner, we developed a new measure, which we term
potential partner. We have upper- and lower-bound definitions of potential partner, termed
maximum potential partners and minimum potential partners respectively. These measures
impose restrictions on age and marital status that do not appear in the POSSLQ measures, but
they impose no restrictions on the number of adults in the household. The minimum potential
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partner measure also imposes restrictions on the relationship to householder. The definitions for
these measures appear in Table 3.
The definition of potential partners differs slightly from the POSSLQ rules. We restricted
potential partners to persons aged 17 or more. Unmarried partners under 17 are extremely rare;
exclusion of persons aged 15 or 16 eliminates a trivial percentage of cohabiting couples while
greatly reducing the number of cases falsely identified as potential partners. We also eliminated
currently married persons as potential unmarried partners. The 2000 census microdata do not
include any married persons listed as unmarried partners, presumably because of post-
enumeration editing. Because married persons were apparently ineligible to be unmarried
partners in 2000, we made them ineligible in earlier years as well.
Table 3. Rules for Identifying Potential Unmarried Partners
MAXIMUM POTENTIAL PARTNER (Upper bound)
a. Must be age 17 or older and opposite sex as the householder
b. Must be first unrelated person listed in the household
c. Neither householder nor partner can be currently married
MINUMUM POTENTIAL PARTNER (Lower bound)
a. Must be age 17 or older and opposite sex as the householder
b. Must be first unrelated person listed in the household
c. Must be listed as partner, roommate, or friend
d. Neither householder nor partner can be currently married
For the lower-bound minimum potential partner measure, we also restricted the
relationship categories for potential partners. POSSLQ and Adjusted POSSLQ allow any
unrelated person to be a partner, as long as they are at least fifteen and of the opposite sex as the
householder. We consider it unlikely that a true unmarried partner prior to 1990 would have been
enumerated as an employee, boarder, or lodger. We therefore restricted the minimum potential
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partners to the categories of partner, friend, housemate, or roommate (see the Appendix for
details on the census relationship question in each census year).
If cohabitors in the period from 1960 through 1980 frequently identified themselves as
lodgers or domestic servants, the minimum potential partner measure would understate the
cohabitation in that period. If, however, we are correct in thinking that few people listed as
lodger or employee in 1960, 1970, or 1980 would have identified themselves as unmarried
partner if that response had been offered on the census form, then the minimum potential partner
measure is justified.
In one respect, we broadened the POSSLQ definition. A substantial number of unmarried
partners reside in households that contain multiple adults, and the prohibition of such households
may significantly bias the characteristics of cohabitors. We therefore have no restriction on the
number of related or unrelated adults in the household. We did, however, impose a rule that the
potential unrelated partner must be the first-listed person in the household who is unrelated to the
householder. Virtually all unmarried partners in 2000 (99.4 percent) were in fact the first
unrelated person listed. In the few cases with preceding unrelated individuals in the household,
we suspect that these unmarried partners are not actually unmarried partners of the householder,
but rather unmarried partners of another unrelated adult. Moreover, by imposing this rule we
limit each household to a single potential partner, which simplifies analysis.
Figure 4 compares the potential partner measures with the POSSLQ measures and with
the unmarried partner variable. Of the four measures, the original POSSLQ comes closest to
matching the number of unmarried partners in 1990 and 2000, but this apparent reliability is
deceptive. Table 4 shows the number of false positives and false negatives for each of the four
measures. False positives are households identified by each measure that do not include an
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unmarried partner; false negatives are households with unmarried partners that are not identified
by each measure. The original POSSLQ fares well only because the high percentage of false
positives is canceled out by the high percentage of false negatives. The Adjusted POSSLQ
reduces the false negatives significantly, but at the price of a high rate of false positives. Our
maximum potential partner misses fewer unmarried partners than the POSSLQ measures, and
our minimum potential partner measure also substantially reduces the number of falsely
identified partners.
Figure 4. Comparison of POSSLQ, potential Partners, and unmarried partners,
1960-2000
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
1960 1970 1980 1990 2000
Census year
Number of couples (000s)
POSSLQ
Adjusted POSSLQ
Maximum potential partners
Minimum potential partners
Umarried Partner
12
Table 4. Error rates for alternate inferred measures of cohabitation
a. False b. False c. Total error
positive negative (a+b)
1990
POSSLQ 25.8 22.7 48.5
Adjusted POSSLQ 28.6 8.5 37.1
Maximum Potential Partner 28.9 5.8 34.7
Minimum Potential Partner 20.7 5.8 26.5
2000
POSSLQ 23.4 20.0 43.4
Adjusted POSSLQ 25.9 6.2 32.1
Maximum Potential Partner 25.8 0.7 26.5
Minimum Potential Partner 16.2 0.7 16.9
Note: false positive is the percent of households identified by the measure that do
not include an unmarried partner; false negative is the percent of households with
unmarried partners not identified by measure.
Our goal for the potential partner measures was to make the definition as narrow as
possible without discarding a significant number of unmarried partners. In 1990, however, our
measures fail to identify 5.8 percent of the opposite-sex unmarried partners listed in the census
microdata. Two-thirds of these cases were excluded based on the marital status rule we imposed
for consistency with Census 2000. As noted, Census 2000 editing procedures did not permit
persons who were currently married to be listed as unmarried partners. Some of these cases, no
doubt, actually represent cohabitors, but the Census 2000 editing rule may be sound: many of
these married cohabitors probably represent coding errors. Excluding false negative cases that
were edited in Census 2000, the 1990 potential partner measures would yield just 1.9 percent
false negatives.
4
4
The remaining false negatives among potential partners in 1990 occurred because the unmarried partner
was not the first-listed unrelated person in the household or because the head or partner was under age 17. In many
of these cases, however, we suspect that the relationship may be miscoded.
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Extending these measures backwards in time highlights the inappropriateness of inferring
cohabitation for persons listed as boarders, lodgers, and employees. Figure 5 shows the
percentage of all couple households (married and unmarried couple households) that are
estimated to include unmarried couples according to each of the four methods, for the entire
period 1880 through 2000. Figure 6 shows the same statistics for the period from 1880 to 1960.
According to most of the measures, the 1960 census represented the low point of cohabitation,
and cohabitation was much more common in the early-twentieth century. This is not because
cohabitation actually declined over the first half of the twentieth century. Rather, these measures
reflect that boarding, lodging, domestic service, and farm labor were much more common before
1950, and often involved residence with unrelated persons of the opposite sex (Goeken 1999).
In the period before 1940, we have access to the actual words used by enumerators to
describe living arrangements. We have recorded 28 cases listed explicitly as concubine or
mistress, several hundred companions, and several thousand partners and friends (most of whom
were apparently business partners). It may have occasionally happened that an enumerator would
record lodger or servant for a person who acknowledged cohabitation, but it was probably rare.
In all periods, the number of cohabitors erroneously enumerated as boarders or employees must
have represented a tiny minority of total persons enumerated in these categories.
14
Figure 5. Unmarried couples as a percentage of all couple households, 1880-2000
0
2
4
6
8
10
12
1880 1910 1910 1920 1940 1950 1960 1970 1980 1990 2000
Census year
Percent of all couple households
POSSLQ
Adjusted POSSLQ
Maximum potential partners
Minimum potential partners
Figure 6. Unmarried couples as a percentage of all couple households, 1880-1960
0.0
0.5
1.0
1.5
2.0
2.5
1880 1910 1910 1920 1940 1950 1960
Census year
Percent of all couple households
POSSLQ
Adjusted POSSLQ
Maximum potential partners
Minimum potential partners
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Predicting potential partners
The potential partner measures include virtually all unmarried partners as they were
defined in Census 2000, but they also include a substantial number of households that did not
contain unmarried partners. To refine the measures further, we used binary logistic regression to
impute a set of unmarried partners probabilistically. Our strategy was to predict unmarried
partner status for potential partners in 1990 and 2000, and then to calculate the predicted
probability of being an unmarried partner for all potential partners from 1960 to 2000.
Table 5 describes the variables used in the models. We ran four models, separating male
and female potential partners in each potential partner universe (maximum and minimum
potential partners). The dependent variable in each case is a dichotomous variable indicating
whether or not a potential partner was an unmarried partner. We selected the independent
variables for their predictive power, and the relationships differ from those cited in the literature
on cohabitation. Most studies contrast cohabitors and married couples (Smock and Manning
2004); our analysis seeks to identify the characteristics that distinguish roommates or other
unrelated persons from unmarried partners. We include census year in the model, since the
overall proportion of potential partners who were actually unmarried partners increased slightly
between 1990 and 2000. We tested for interactions between census year and the other
independent variables but did not find any significant relationships.
The regression results are shown in Table 6. The strongest predictors of unmarried
partner status were age difference between householder and potential partner, number of adults
in household, presence of own children, presence of children under five, home ownership, age,
and census year.
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Table 5. Independent variables for regression analyses
Variable short name Variable description
Household
Year Census year (coded 100 for 2000, 99 for 1990, 98 for 1980 and so on)
Region Region (dummy variables: Northeast, Midwest, South and West)
Metro Households residing in a metropolitan area, as defined in each census
year (coded 1=yes and 0=no)
Owns Housing unit is owned (coded 1=yes and 0=no)
Num of Adults Number of other adults in the household in addition to householder and
potential partner and excluding adult children
Person
Div-sep Potential partner is divorced or separated (coded 1=yes and 0=no)
HH div-sep Householder divorced or separated (coded 1=yes and 0=no)
Child Potential partner's own child(ren) present (coded 1=yes and 0=no)
HH child Householder's own child(ren) present (coded 1=yes and 0=no)
HH child5 Householder's own child(ren) under age 5 present (coded 1=yes and
0=no)
Age Potential partner age groups (dummy variables; see regression)
Age diff Age difference between the householder and potential partner (dummy
variables; see regression)
School Potential partner in school (coded 1=yes and 0=no)
HH school Householder in school (coded 1=yes and 0=no)
Education Potential partner's educational attainment (dummy variables: has not
finished high school, completed high school, some college, and 4+ years
of college)
Educational diff. Difference in educational attainment levels between householder and
partner
HH income Householder's income in 1000s--adjusted to 2000$; topcode of 150,000
(1960 topcode in 2000$); all negative values coded 0
Income diff. Difference in householder's and potential partner's income (measured as
above)
Unemployed Potential partner is unemployed (coded 1=yes and 0=no)
HH unemp. Householder is unemployed (coded 1=yes and 0=no)
Not in labforce Potential partner is not in the labor force (coded 1=yes and 0=no)
HH not in labforce Householder is not in the labor force (coded 1=yes and 0=no)
When we use the coefficients in Table 6 to estimate the predicted number of unmarried
partners in earlier census years, the results suggest that previous estimates of cohabitation before
1990 may be dramatically overstated. Figure 7 compares our predicted number of unmarried
partners in each census year with the number of POSSLQ households. In 1980, our maximum
estimate of unmarried partners is two thirds of the Adjusted POSSLQ measure, and in 1960 and
1970 our maximum estimate is less than half that obtained from Adjusted POSSLQ. Our
17
Table 6. Binary logistic regressions of unmarried partner status:
potential partners, 1990-2000
Minimum potential partners Maximium potential partners
Male partners Female partners Male partners Female partner
s
V
ariables Exp(B) Exp(B) Exp(B) Exp(B)
Year 1.399 *** 1.335 ***
1.197 *** 1.114 ***
Region
Northeast
Midwest 0.942 0.944
0.927 *** 0.944 ***
South 0.816 *** 0.848 ***
0.822 *** 0.854 ***
West 0.737 *** 0.772 *** 0.785 *** 0.816 ***
Metro 0.836 *** 0.836 *** 0.809 *** 0.825 ***
Ownership 1.338 *** 1.344 *** 1.136 *** 1.153 ***
Num. of adults 0.626 *** 0.659 *** 0.582 *** 0.623 ***
Div-sep 1.057 1.023 1.057 *** 0.976 ***
HH div-sep 1.079 * 1.107 **
1.084 *** 1.134 ***
Child 1.499 0.895 1.066 0.830 ***
HH child 1.646 *** 1.975 *** 1.233 *** 1.787 ***
HH child5 1.519 *** 1.714 *** 1.586 *** 1.970 ***
Chid*div-sep 0.946 1.402 ** 1.118 ** 1.429 ***
HHchild*HHdiv-sep 0.769 *** 0.669 *** 0.784 *** 0.545 ***
Age
17-19
20-24 1.270 * 0.883
1.284 *** 0.957 ***
25-29 1.344 ** 0.934 1.370 *** 1.031 ***
30-34 1.257 * 0.866 1.271 *** 0.977 ***
35-39 1.249 * 0.843 * 1.208 *** 0.908 ***
40-44 1.104 0.843 * 1.036 *** 0.875 ***
45-49 0.989 0.790 **
0.847 *** 0.791 ***
50-59 0.873 0.583 *** 0.647 *** 0.580 ***
60-69 0.664 ** 0.469 *** 0.462 *** 0.408 ***
70-79 0.575 *** 0.384 *** 0.372 *** 0.347 ***
80+ 0.469 *** 0.323 *** 0.285 *** 0.260 ***
Age diff.
less than -35 0.873 0.417
0.428 *** 0.268 ***
-34 thru -30 0.761 0.095 0.731 *** 0.045 ***
-29 thru -25 0.904 0.362 ** 0.839 *** 0.264 ***
-24 thru -20 0.787 0.498 ** 0.920 *** 0.386 ***
-19 thru -15 0.970 0.753 1.005 0.655 ***
-14 thru -10 1.178 * 0.816 * 1.215 *** 0.878 ***
-9 thru -5 1.072 0.913 1.079 *** 0.959 ***
4 thru -2 1.042 0.939
1.032 *** 0.960 ***
-1 thru 1
2 thru 4 0.906 * 1.135 **
0.890 *** 1.105 ***
5 thru 9 0.737 *** 1.018 0.694 *** 1.001
10 thru 14 0.580 *** 0.851 ** 0.489 *** 0.818 ***
15 thru 19 0.390 *** 0.722 *** 0.224 *** 0.622 ***
20 thru 24 0.189 *** 0.483 ***
0.074 *** 0.348 ***
25 thru 29 0.110 *** 0.452 *** 0.033 *** 0.255 ***
30 thru 24 0.082 *** 0.282 *** 0.022 *** 0.135 ***
35 + 0.082 *** 0.299 *** 0.012 *** 0.066 ***
School 0.764 *** 0.820 *** 0.760 *** 0.805 ***
HH school 0.767 *** 0.688 *** 0.792 *** 0.726 ***
Education ***
Some high school 1.623 *** 1.479 ***
1.308 *** 1.203 ***
Completed high school 1.384 *** 1.282 *** 1.184 *** 1.131 ***
Some college 1.224 *** 1.258 *** 1.142 *** 1.167 ***
4+ years of college
***
Educational diff. 0.960 * 0.908 ***
0.971 *** 0.929 ***
HH income 1.007 *** 1.006 *** 1.006 *** 1.004 ***
Income diff. 0.997 *** 0.998 *
0.997 *** 0.999 ***
Unemployed 1.105 0.951 1.010 * 0.895 ***
HH unemployed 0.967 0.857 * 0.955 *** 0.845 ***
Not in labforce 0.886 ** 0.965 0.897 *** 0.785 ***
HH not in labforce 0.934 0.814 *** 0.777 *** 0.916 ***
Constant 0.000 *** 0.000 *** 0.000 *** 0.000 ***
18
Figure 7. Predicted partners compared with POSSLQ measures, 1960-2000
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
1960 1970 1980 1990 2000
Census year
Number of couples (000s)
POSSLQ
Adjusted POSSLQ
Predicted partners-maximum
Predicted partners-minimum
Figure 8. Predicted partners compared with POSSLQ measures, 1960-2000
(log scale)
1
10
100
1,000
10,000
1960 1970 1980 1990 2000
Census year
Number of couples (000s)
POSSLQ
Adjusted POSSLQ
Predicted partners-maximum
Predicted partners-minimum
19
minimum estimates—which we consider more realistic—are so small that they are difficult to
see on the graph in the early census years.
Figure 8 presents the same data as Figure 7 on a log scale, to allow easier comparison.
Our minimum measure suggests that just 8,000 people in 1960 would have listed themselves as
unmarried partners had the category been available, 78,000 in 1970, and just over a million in
1980. Many more couples in 1960 must have been living together without being legally married,
but because of the stigma associated with cohabitation in that period, these couples may have
reported themselves as husband and wife. In other cases, respondents may simply have neglected
to acknowledge the presence of an unmarried partner.
5
Our goal, however, is to estimate self-
identified unmarried partners. The low number of cohabitors in 1960 estimated by the model
may indeed approximate the number of persons who identified themselves as unmarried couples.
Discussion
This analysis expands the chronological scope of research on cohabitation in the United
States. We hope that these estimates will provide a baseline for understanding one of the most
profound changes in household formation of the late twentieth century. These estimates can also
provide further insight into other demographic phenomena, such as rising marriage ages and the
uncoupling of nuptiality and fertility. Our approach moves beyond the simple set of rules used in
both versions of the POSSLQ measure; instead, our analysis of the 1990 and 2000 census years
examines which characteristics distinguish unmarried partners from roommates (or other groups
of unrelated persons). Instead of a simple dichotomy, the predicted probability approach
provides a continuous measure and new analytic possibilities.
5
We consider it more likely that cohabiting opposite-sex couples in 1960 were reported as spouses or omitted than
that they were reported as employees or boarders. The more inclusive measures of cohabitation, such as POSSLQ,
cannot account for such misreporting any more than does our minimum potential partner measure.
20
Previous estimates of pre-1990 cohabitation have understated the magnitude and pace of
change during the period from 1960 to 1990. The published estimates for 1960 and 1970
overstate the number of households that meet the POSSLQ definition. More important, the
POSSLQ and Adjusted POSSLQ definitions greatly overstate cohabitation before 1990. Even if
it is justified to count relationship types such as boarders and domestic servants as cohabitors, the
POSSLQ measures probably overstate cohabitation in 1960 and 1970 by at least a factor of two.
We favor a more conservative approach that focuses on self-identified cohabitation. By this
standard, the traditional measures overstate cohabitation before 1980 by an order of magnitude.
These revisions make a significant difference. Table 7 summarizes the estimates
presented in Figures 1, 2, 4, and 7. The widely-accepted published POSSLQ measures suggest an
increase in cohabitation of just over 10-fold between 1960 and 2000. Our predicted partner
measure, by contrast, implies an increase between 28-fold (under the upper-bound universe) and
576-fold (under the lower-bound universe). The timing of change also varies by estimation
method. According to the more inclusive methods, there were already several hundred thousand
cohabitors by 1960 but there was only a modest rise in cohabitation during the 1960s. Under our
lower-bound estimates, however, there was very cohabitation in 1960, and there was a dramatic
increase (in percentage terms) during the following decade.
Our methods improve the potential for individual-level analysis of cohabitation in the
pre-1990 censuses. The POSSLQ measures are of limited use for this purpose, since they
introduce substantial biases with respect to household size, education, race, and presence of
children (Baughman, Dickert-Conlin, and Houser 2002). Our preliminary analysis suggests that
these problems are dramatically reduced for predicted partners, using either the lower-bound or
21
upper-bound universe. In future work, we plan to use these measures to assess changes in the
characteristics of cohabitors during the 1960s and 1970s.
Table 7. Comparison of cohabitation estimates, 1960-2000
Percent change
1960 1970 1980 1990 2000
1960-
2000
1990-
2000
POSSLQ, published 439 523 1,589 2,856 4,746 1,081 166
POSSLQ, corrected 280 430 1,759 3,232 4,861 1,736 150
Adjusted POSSLQ 399 575 2,077 3,975 5,900 1,479 148
Potential partners-maximum 437 485 2,127 4,110 6,219 1,423 151
Potential partners-minimum 17 128 1,412 3,686 5,505 32,382 149
Predicted partners-maximum 164 230 1,428 2,923 4,615 2,814 158
Predicted partners-minimum 8 78 1,042 2,923 4,613 57,663 158
Opposite sex unmarried partners 3,102 4,646 150
Unmarried partners, restricted*
2,982 4,646
156
*Opposite sex unmarried partners under Census 2000 editing rules (both partners currently married).
We have not yet addressed the issue of same-sex unmarried partners. We plan to apply
similar techniques to analyze this population, but we are not optimistic about our prospects for
successfully identifying same-sex cohabitors before 1980. We suspect that it will be difficult to
distinguish same-sex unmarried partners from roommates and business partners. Nevertheless,
because of the importance of the topic and the paucity of alternative sources, it is worth
investigating the feasibility of historical analysis.
22
Works Cited
Baughman, Reagan, Stacy Dickert-Conlin, and Scott Houser. 2002. “How Well Can We Track
Cohabitation Using the SIPP? A Consideration of Direct and Inferred Measures,”
Demography 39(3):455-465.
Bumpass, Larry L., James A. Sweet, and Andrew Cherlin. 1991. “The Role of Cohabitation in
Declining rates of Marriage,” Journal of Marriage and the Family 53: 913-27.
Bumpass, Larry L. and Hsien-Hen Lu. 2000. “Trends in Cohabitation and Implications for
Children’s Family Context in the United States,” Population Studies 54: 29-41.
Bumpass, Larry L. and James A. Sweet. 1989. “National Estimates of Cohabitation,”
Demography 26: 615-25.
Casper, Lynne M. and Philip N. Cohen. 2000. “How Does POSSLQ Measure Up? Historical
Estimates of Cohabitation” Demography 37(2): 237-245.
Casper, Lynne M. and Suzanne M. Bianchi. 2002. Continuity and Change in the American
Family. Thousand Oaks, CA: Sage.
Chevan, Albert. 1996. “As Cheaply as One: Cohabitation in the Older Population.” Journal of
Marriage and the Family 58:656-667
Glick, Paul C. and Arthur .J. Norton. 1977. “Marrying, Divorcing and Living Together in the
U.S. Today,” Population Bulletin 32(1):4-34.
Glick, P.C. and G.B. Spanier. 1980. “Married and Unmarried Cohabitation in the United States,”
Journal of Marriage and Family 42: 19-30.
Goeken, Ron. 1999. Unmarried Adults and Residential Autonomy: Living Arrangements in the
United States, 1880-1990. Dissertation: University of Minnesota.
Hatch, Rebecca Gronvold. 1995. Aging and Cohabitation. New York:Garland.
Manning, Wendy D. 1995. “Cohabitation, Marriage and Entry into Motherhood,” Journal of
Marriage and the Family 57: 191-2000.
Moffitt, Robert A., Robert Reville, and Anne E. Winkler. 1998. “Beyond Single Mothers:
Cohabitation and Marriage in the AFDC Program.” Demography 35(3):259-278.
Ruggles, Steven. 1995. “Family Interrelationships,” Historical Methods 28: 52-58.
Ruggles, Steven and Susan Brower. 2003. “The Measurement of Family and Household
Composition in the United States, 1850-2000.” Population and Development Review
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Kelly Hall, Miriam King, and Chad Ronnander. Integrated Public Use Microdata Series:
Version 3.0 [Machine-readable database]. Minneapolis, MN: Minnesota Population
Center [producer and distributor], 2004.
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Smock, Pamela J. and Wendy Manning. 2004. “Living Together Unmarried in the United States:
Demographic Perspectives and Implications for Family Policy.” Law and Policy 26: 87-
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Characteristics”. Washington, D.C.: U.S. Government Printing Office.
24
Appendix:
Census Questions on Unrelated Household Members
1960-2000
Relationship information in the 1960 census
Write names in this order
Head of household on first line
Wife of head
Unmarried children, oldest first
Married children and their families
Other relatives
Others not related to head of household If "Other not related to
head," also
give exact relationship, for example, partner, maid, etc.
What is the relationship of each person to the head of this
household? (For example, wife, son, daughter, grandson, mother-
in-law, lodger, lodger's wife)
____________________
Relationship information in the 1970 census
O Head of household
O Wife of head
O Son or daughter of head
O Other relative of head - Print exact relationship
______________________________
O Roomer, boarder, lodger
O Patient or inmate
O Other not related to head - Print exact relationship
____________________________
If "Other not related to head," also
give exact relationship, for example, partner,
maid, etc.
If two or more unrelated people live together and share the rent, mark the first
one you list Head of household. Mark the rest Other not related to head
and print "partner" in the space. A stepchild or legally adopted child of the
head should be marked Son or daughter."
25
Relationship information in the 1980 census
If not related to person in column 1:
O Roomer, boarder
O Partner, roommate
O Paid employee
O Other nonrelative _______________
"Fill a circle to show how each person is related to the person in
column 1. A stepchild or legally adopted child of the person in
column 1 should be marked Son/daughter. Foster children or wards
living in the household should be marked Roomer, boarder."
1990-2000 “unmarried partner” category
Relationship to householder question:
How is this person related to person 1?
If not related to person 1:
O Roomer, boarder
O Housemate, roommate
O Unmarried partner
O Foster child
O Other nonrelative
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