ESTIMATES ABOUT FERTILITY AND GRANDPARENTS FROM THE ACS, THE CPS, C2SS,
AND CENSUS 2000

Martin O'Connell

Gretchen Gooding

HHES Division

U.S. Census Bureau

*This report is released to inform interested parties of ongoing
research and to encourage discussion of work in progress. The views
expressed on the statistical and methodological issues in this report
are those of the authors and not necessarily those of the U.S. Census
Bureau.*

ESTIMATES ABOUT FERTILITY AND GRANDPARENTS FROM THE ACS, THE CPS, C2SS,
AND CENSUS 2000

# INTRODUCTION 

This report compares national distributions based on data from the
American Community Survey (ACS) with those based on data from various
Census Bureau surveys for two items: fertility (women who gave birth in
the past 12 months) and grandparents residing with their grandchildren.
This report first compares estimates of the number of women who gave
birth in the 12 months preceding the survey date based on the 2004 ACS
with estimates based on the 2004 June Fertility Supplement to the
Current Population Survey (CPS). It then notes variations that are both
statistically and substantially different, and for those found, offers
possible explanations.

The second analysis compares estimates of the number of grandparents
living with grandchildren under 18, if they are primarily responsible
for the care of their grandchild, and the duration of their
responsibility. The 2004 ACS data on grandparents are compared with
Census 2000 sample data and the Census 2000 Supplementary Survey (C2SS)
data because the Census 2000 data constitute the most comparable data.
For the analysis of both fertility and grandparents, the universe is
restricted to people recorded as living in households.

# METHODOLOGY

The tables included in this report compare the most commonly tabulated
data on fertility and grandparents from the ACS, the CPS, C2SS, and
Census 2000. Comparisons consist primarily of percentage-point
differences between the ACS and all other comparison distributions.
Tables display the survey estimates, the margins of error from which
90-percent confidence intervals of the estimates can be derived, and the
difference between the estimates. In the case of frequency
distributions, the difference is calculated as the percent difference
between the two estimates. In the case of relative frequency
distributions, the difference is calculated as the percentage-point
difference between the two estimates. An asterisk (\*) denotes
statistically significant differences.

At the national level, survey variances were small, resulting in many
statistically significant differences between the distributions. This
report focuses on statistically significant differences of 0.5
percentage points or more. This yardstick can vary based on the relative
size of the category. For example, for population groups constituting a
relatively large percentage of the population (such as children born to
women with at least one year of college), a 0.5 percentage-point
difference in the estimates might be relatively small, while for
population groups constituting a smaller percentage of the population
(such as children born to women who have not completed high school), a
0.5 percentage-point difference could be relatively large. Users may
choose statistically significant differences that are smaller or larger
than 0.5 percentage points for their own analytical purposes.

The remainder of this section examines differences in methodology
between these different data sets.

# Sample Frame

The 2004 ACS surveyed a national sample of housing units, both occupied
and vacant. An initial sample of 838,000 households resulted in 569,000
completed interviews. Data were collected in a total of 1,240 counties
of the 3,141 counties in the United States. The sample is designed to
provide estimates of housing and socio-economic characteristics for the
nation, all states, most areas with a population of 250,000 or more, and
selected areas of 65,000 or more.

The 2004 June CPS surveyed a national sample of approximately 51,000
households in 792 primary sampling units. The sample is designed to
produce estimates of the labor force characteristics of the civilian
noninstitutionalized population 16 years of age and older for the nation
and all states.[^1]

One difference between the ACS and the CPS survey universes is that the
CPS includes a small number of individuals living at addresses that were
housing units in 2000 but have since been converted into
noninstitutional group quarters (e.g. emergency and transitional
shelters and group homes). For the purposes of this report, all
individuals with detailed household and family status of "in group
quarters" (HHDFMX = 51) were excluded from the CPS estimates for all
comparisons shown on this report.

The long-form questionnaire used in Census 2000 was sent to a sample of
approximately 1-in-6 households. This sample was designed to produce
national, state, and substate estimates of many social and economic
characteristics from questions that were not included on the Census 2000
short-form that was sent to the entire population.[^2]

The C2SS was conducted as part of Census 2000 to demonstrate the
operational feasibility of ACS methods. The C2SS distributions in this
report come from information collected in the year 2000 from the
original 36 ACS test counties plus another sample of 1,203 counties
selected and surveyed using current ACS operational and data collection
methods.[^3]

# Sample Size and Mode of Data Collection

The 2004 ACS interviewed a total of 534,383 occupied households. Data
were collected continuously throughout the year using a combination of
mail-out/mail-back questionnaires, Computer-Assisted Telephone
Interviewing (CATI), and Computer-Assisted Personal Interviewing (CAPI).
Each month a unique national sample of addresses received an ACS
questionnaire. Addresses that did not respond were telephoned during the
second month of collection if a phone number for the address was
available, and personal visits were conducted during the third month and
the last month of data collection for a subsample of the remaining
nonresponding units. The 2004 ACS achieved an overall survey response
rate of 93.1 percent, calculated as the initially weighted estimate of
interviews divided by the initially weighted estimate of cases eligible
to be interviewed.

The 2004 June CPS contained interviews from about 51,000 households. The
fertility items were included in a supplement to the June CPS that was
conducted during the third week of June 2004. All CPS data are collected
via Computer-Assisted Telephone and Personal Interviews (CATI/CAPI),
with interviews conducted during one week each month. The response rate
for the basic 2004 June CPS was 92 percent. Both the ACS and the CPS
employ experienced, permanent interviewers for CATI and CAPI data
collection.

The Census 2000 Supplementary Survey (C2SS) used the same methods as the
2004 ACS. The unit survey-response rate for the C2SS was 95.1 percent.
In Census 2000, the sample households had a unit survey-response rate of
91.2 percent.[^4]

# Residence Rules

The ACS, the CPS, C2SS, and Census 2000 used different residence rules
to determine which individuals in a household would be eligible for
interview. This difference may contribute to variation in the universes
from which the social characteristics are measured.

The ACS and C2SS used identical rules. These surveys collected
interviews from everyone in the sample housing unit on the day of
interview who was living or staying there for more than two months,
regardless of whether or not they maintained a usual residence elsewhere
or if they did not have a usual residence. If a person who usually lived
in the housing unit was away for more than two months at the time of the
survey contact, he or she was not considered to be a current resident of
that unit. This rule recognizes that people can have more than one place
where they live or stay over the course of a year, and these people can
affect the estimate of the characteristics of the population for some
areas. However, at high geographic levels such as the nation or the
state, it is not expected that these rules would affect survey
estimates.

The CPS interviews all people staying in the housing unit at the time of
the interview who consider the housing unit to be their usual residence
or who have no usual residence. The CPS also includes temporarily absent
individuals who consider the housing unit as their usual residence.

The different residence rules result in one notable difference in the
universes of these two surveys. Because the 2004 ACS and C2SS excluded
group quarters from the sample frame and interviewed individuals at
their current residence, college students living in dormitories were not
included in the ACS universe. In contrast, the CPS interviewers were
instructed to include as household members any college students who were
temporarily absent from the household, including those who were
currently residing in college dormitories. The resulting CPS sample
universe included more college students than the ACS sample universe,
even if they lived most of the year away from their parent's home in a
school dormitory.

For Census 2000, each person was enumerated as an inhabitant of his or
her "usual residence." Usual residence is the place where the person
lives and sleeps most of the time. If a person had no usual residence,
the person was to be counted where he or she was staying on Census Day
(April 1, 2000). Unlike the CPS, college students were counted as
residents of the area in which they were living while attending college.
Children in boarding schools below the college level were counted at
their parental home. For Census 2000, people living in group quarters
were included in the Census enumeration, but they were excluded in the
analysis in this paper.

# Question Wording and Reference Periods

# Differences between the ACS, the CPS, C2SS, and Census 2000 in presentation and wording of questions may contribute to differences in estimates. 

# *Fertility.* The 2004 American Community Survey asked the following fertility question of all women 15 to 50 years old:

> Has this person given birth to any children in the past 12 months?
>
> Yes
>
> No

This question was asked each month in the ACS over the 12 calendar
months; therefore, the data included information referring to periods
before 2004.

The June 2004 supplement to the CPS asked the fertility question to
women 15 to 44 years old in two parts. First:

> How many live births, if any, have you ever had?
>
> None
>
> Number of children \_\_\_\_

Second, for women who had ever had one or more births, the date of the
last-born child was asked as follows:

In what month and year was your (child/last child) born?

Enter month

Enter year \_\_\_\_

If a woman reported a date of last birth between July 2003 and June
2004, then she was categorized as having had a birth in the last 12
months. In this report, estimates from this sample population will be
compared with estimates from the ACS sample population described above.

Several important differences exist between these two surveys. First,
the ACS surveys women 15 to 50 years of age, while the CPS surveys women
15 to 44 years. In recent years, about 6,000 women aged 45 to 50 have
given birth each year, out of a total of 4 million women having a birth.

Second, the ACS estimate for 2004 refers to women answering the question
in the period January to December 2004 for the 12-month period prior to
the survey date. This means that a person answering in January 2004 may
be responding "Yes" to a birth that happened as far back as January
2003. In the CPS, births in the last 12 months are tabulated as those
recorded between July 2003 and June 2004. However, since the CPS is
always conducted during the week that contains the 19^th^ day of the
month, births occurring in the last week of June (which could account
for about 2 percent---80,000---of all births in a 12-month period) were
not tallied in the 12-month estimate.

Estimates from the CPS and the ACS may vary because of the different
reference periods and ages of women being asked the questions and
because the wording and the complexity of the questions differed. To
determine if a woman had a birth in the last 12 months, two questions
were asked in the CPS, compared with one in the ACS. The ACS data may
overestimate the number of women who gave birth in the 12-month period.
For example, some women answering the question as "Yes" in May 2004 may
have given birth in the early days of May 2003, and hence, may have had
their child some days or weeks more than 12 months prior to the
interview date.

***Grandparents.*** Three grandparent items were asked in the ACS, C2SS,
and Census 2000, using identical wording and response categories. All of
the surveys asked the questions of people 15 and older, although the
data were tabulated only for people 30 and older due to the low
probability of a person under age 30 being a grandparent. In both the
ACS and C2SS, follow-up interviews (which made up approximately 40
percent of all interviewed households using the CAPI/CATI instrument),
people under age 30 were skipped out of this series of questions. The
items were asked as follows (the item numbers are used here only to
demonstrate the skip patterns used in this series of questions):

1a. Does this person have any of his/her own grandchildren under the age
of 18 living in this house or apartment?

> Yes
>
> No\-\--skip to question 2

1b. Is this grandparent currently responsible for most of the basic
needs of any grandchild(ren) under the age of 18 who live(s) in this
house or apartment?

Yes

No\-\--skip to question 2

1c. How long has this grandparent been responsible for the(se)
grandchild(ren)?

If the grandparent is financially responsible for more than one
grandchild, answer the question for the grandchild for whom the
grandparent has been responsible for the longest period of time.

Less than 6 months

6 to 11 months

1 or 2 years

3 or 4 years

5 or more years

# Item Nonresponse

Item nonresponse occurs when an individual does not provide complete and
usable information for a data item. Item allocation rates are often used
as a measure of the level of item nonresponse. Allocation rates are
computed as the ratio of the number of eligible people for which a value
was allocated during the editing process for a specific item to the
number of people eligible to have responded to that item.

***Fertility.*** For the 2004 ACS, the allocation rate for the single
fertility item for women 15 to 50 years old was 1.7 percent. For the
CPS, the allocation rate for the children-ever- born item for women 15
to 44 years old was 10.9 percent. Among women with one or more children
ever born, the allocation rate for the date of birth of the last-born
child was 18.1 percent. The need for two pieces of information to
identify a birth in the last year in the CPS, including a specific month
and year of the birth, may have affected the quality of the data.

***Grandparents.*** The 2004 ACS rules for assigning allocation flags
for missing/inconsistent data on the grandparent items differed from
those in either the C2SS or Census 2000. In the 2004 ACS, if a person
answered that they were a coresident grandparent or left the item
unanswered, and if they lived in a household where there was no person
under 18 who could possibly be their grandchild, that person was
assigned a "No" response and their response was flagged as being
"assigned" for household consistency reasons. This situation was not
treated as an allocated response.[^5] For the same situation in the C2SS
and Census 2000, this same type of response was also assigned a "No"
value but was treated as being "allocated," creating different
allocation rates.

In the 2004 ACS, the allocation rate for the first grandparent item was
0.4 percent, compared with 4.6 percent in the C2SS and 6.0 percent in
Census 2000. For the remaining two items, ACS item nonresponse was also
lower, even though editing procedures and allocation assignments were
more consistent. For the grandparent-responsibility item, the ACS
allocation rate was 10.3 percent, compared with 17.6 percent in the C2SS
and 15.3 percent in Census 2000. For the duration-of-responsibility
item, the ACS allocation rate was 10.9 percent, compared with 19.7
percent in the C2SS and 17.8 percent in Census 2000.

A difference in data collection procedures could account for some of the
differences in nonresponse rates. The ACS and C2SS data were partly
collected using a CATI/CAPI instrument that had internal consistency
checking routines, possibly reducing errors from being recorded in the
field collection of the data. No CATI/CAPI instrument was used in the
Census 2000 sample. In all three surveys, imputation rates for these
items were generally higher than for other basic demographic items such
as age, sex, and relationship. Whenever a person's age or relationship
item in any of these surveys was imputed or altered, it opened the
possibility that a grandchild would be created or changed to another
relationship category, thus creating the potential for inconsistencies
in reporting patterns.

One example would be a 3-year-old with a missing relationship category
who is imputed to be the grandchild of the householder. Assigning that
3-year old to be a grandchild triggers a series of required answers,
none of which were originally recorded and none of which would be
accurate if the child were not, in fact, a grandchild. Hence, an
imputation is flagged for this householder because a grandchild was
imputed in the relationship editing step.

# 

# Data Editing and Imputation Procedures

# The ACS, the CPS, C2SS, and Census 2000 edit and imputation rules are designed to ensure that the final edited data are as consistent and complete as possible. These rules are used to identify and account for missing, incomplete, and contradictory responses. In each case where a problem is detected, pre-established edit rules govern its resolution.

The four surveys employ two principal imputation methods: relational
imputation and hot deck allocation. Relational imputation assigns values
for blank or inconsistent responses on the basis of other
characteristics on the person's record or within the household. Hot deck
allocation supplies responses for missing or inconsistent data from
similar responding housing units or people in the sample.

The editing procedures for all surveys employ logical checking routines
to produce consistency among household members and other responses. For
example, no person under age 30 can be a grandparent and no person can
be a coresident grandparent if no one else in the household has a
relationship category that would suggest that they are a potential
grandchild of the respondent. When answers cannot be logically assigned
or when inconsistencies or missing data are encountered, allocation
routines using hot decks generally stratify the donors and recipients of
the hot deck by their age, sex, race, and other characteristics of the
household. Because of differences in the sample size of these surveys,
hot decks will vary in the level of detail and the frequency of updating
the individual cells in the hot deck.

# Controls and Weighting 

## There are notable differences among the surveys in the selection of controls and the calculation of weights that may lead to differences in estimates. The ACS, the CPS, C2SS, and Census 2000 samples are weighted to account for both the probability of selection and housing unit nonresponse. 

## 

## After the initial weighting, data from the 2004 ACS, the C2SS, and the 2004 CPS were all controlled to be consistent with independent population estimates. Data from the 2004 ACS and C2SS were controlled at the county level to independent estimates of the population of individuals and housing units using July 2004 and April 2000 controls, respectively. The 2004 June CPS was controlled to independent national estimates of the civilian noninstitutionalized population in June 2004. Because the 2004 ACS and C2SS control to both the total population and the total number of housing units, both files contain both person weights and housing-unit weights. The CPS does not control to the total number of housing units and, thus, the CPS files do not contain an independent housing-unit weight but instead use the weight of the householder as the weight of the housing unit.

After the application of the controls, the CPS data are raked to ensure
that the number of husbands and wives are equal and that the number of
married-couple households equals the number of married-spouse-present
householders. The ACS currently employs no similar raking routine. The
C2SS weighting procedure was the same as the 2004 ACS.

Estimates from the Census 2000 sample were obtained from an iterative
ratio-estimation procedure that assigned a weight to each sample person.
The estimation procedure used to assign the weights was performed in
geographically defined weighting areas that were usually formed of
contiguous geographic units within counties. Within a weighting area,
the long-form sample was ratio-adjusted to equal the 100-percent total
for certain categories such as family households or nonfamily
households, age, sex, race, and Hispanic origin. This procedure resulted
in weights for each person that could vary from person to person within
the same housing unit.

# RESULTS

# Fertility 

Table 1 indicates that the number of women who gave birth in the
12-month period prior to the survey date was about 350,000 more in the
ACS than in the 2004 June CPS. Aside from differences in estimates
resulting from differences in the reference period and the age universe,
the CPS estimates of births typically fall below the level recorded in
the vital statistics system, even after accounting for some of the
differences between survey-based and administrative record systems.[^6]

The ACS estimate of 4,089,000 women who gave birth in the last 12 months
is not statistically different from the preliminary estimate of births
for calendar year 2004 made by the National Center for Health Statistics
using the vital statistics registration system\-- 4,116,000 births or
approximately 4,050,000 women after accounting for births in multiple
deliveries.[^7] Because the ACS estimates of the number of women who
gave birth is larger than the CPS estimates, the comparison of these two
data sets will be presented in terms of the percentage distributions of
women by their characteristics instead of the numbers of women in
different population groups.

A majority of the percent differences shown in Table 1 are statistically
significant at 0.5 percentage points or more, warranting further
examination. The ACS data records a larger percentage of women 35 to 50
years old who gave birth in the past 12 months than does the CPS data
(18.7 percent and 15.9 percent, respectively). As noted previously, the
ACS includes women 35 to 50 years old in this category, while the CPS
includes only women 35 to 44 years old. In recent years, vital
statistics data indicate about 6,000 women aged 45 to 50 give birth each
year out of 4 million (about 1.5 percent of all births), possibly
accounting for the higher percentage of births in the 35-to-50 years age
category in the ACS than in the CPS. At the same time, the CPS indicates
a higher proportion of births to teenage women (10.3 percent) than does
the ACS (6.7 percent). It is not clear why these differences occur for
this particular period.

The older age range of women who gave birth in the ACS may account for
differences in other categories too. These categories include the "Now
married," "Native," "In labor force," and higher educational attainment
categories ("Some college or associate's degree," "Bachelor's degree,"
and "Graduate or professional degree"), which are likely to have higher
percentages of older women. Slightly higher proportions of women with
recent births are in these categories in the ACS than in the CPS.

For example, the ACS has a higher percentage of women in the "Now
married" category than does the CPS (71.4 percent and 68.3 percent,
respectively). Most women 45 to 50 years old are married, and births to
this age group are excluded from the CPS universe, possibly giving the
CPS a lower percentage of now-married respondents compared with the ACS.

Table 1 also notes a higher proportion of White alone women who gave
birth in the last 12 months in the CPS (76.9 percent) than in the ACS
(70.4 percent).[^8]

Differences in marital status may also be attributed to variation in the
interviewing structure. The CPS requires personal or telephone contact
between respondents and interviewers for all households, while personal
or telephone contacts in the ACS are made only for follow-up to
nonrespondent households. The presence or absence of an interviewer may
affect the response patterns for these questions. As the majority of
responses from ACS households are from mail-out/mail-back forms, most
respondents see a list of possible responses to the marital status item
(Now married, Widowed, Divorced, Separated, or Never married). On the
other hand, all data in the CPS are collected via interviewer/respondent
mode, either in-person or by telephone, where the interviewer reads the
possible responses.

Other differences between the ACS and the CPS may be explained by
discrepancies in the reference periods. As previously mentioned, the ACS
estimates refer to women who gave birth in the 12-month period prior to
the survey date (January to December 2004). In the CPS, births in the
last 12-months were tabulated as those recorded between July 2003 and
June 2004. Some of the small but statistically significant differences
may reflect changes in fertility patterns from one year to the next.

Finally, differences in wording and the resultant complexity of
responses may account for differences in reporting between the two
surveys. To determine if a woman gave birth in the last 12 months, two
questions are used in the CPS compared with the single question used in
the ACS. The higher imputation rates on the items used to derive the
estimates in the CPS may adversely affect both the number of estimated
births in the last year and data on the characteristics of the women if
imputation rates differ among population groups.

# Comparison of Grandparents Data

Table 2 compares data on grandparents from three surveys: the 2004 ACS,
the C2SS, and Census 2000. Results from the 2004 ACS are expected to
differ from those from C2SS and the Census sample because the data were
collected 4 years apart. No comparable series of grandparent items has
ever been placed on a CPS supplement. Despite this difference in years,
the data are fairly consistent. Overall, all three data sets indicate
that about 5.6 million to 5.8 million grandparents lived with their
grandchildren, of whom about 2.4 million were primarily responsible for
the grandchildren.

# Grandparents Living with Grandchildren

Table 3 presents data on grandparents living with grandchildren. While
the overall results from the ACS and the Census compare
favorably\--given the difference in years\--a few statistically
significant differences of 0.5 percentage points or more are noted in
the "Race and Hispanic Origin" category.[^9] Principally, the ACS data
indicate a higher proportion of co-resident grandparents who reported
that they were the single-race group White and a lower proportion of
co-resident grandparents who reported that they were the single-race
group Black or African American than were recorded in Census 2000
estimates. The population of grandparents living with grandchildren is
smaller than many other populations (for example, married-couple family
households), possibly resulting in estimates that are more sensitive to
yearly fluctuations. Both the ACS and the Census sample indicate that
almost two-thirds of all co-resident grandparents are grandmothers.

# Grandparents Responsible for Grandchildren 

Table 4 presents data on grandparents responsible for their
grandchildren. Results from the ACS and the Census are again
consistent\--given the difference in years. Statistically significant
differences of 0.5 percentage points or more are again noted in the
"Race and Hispanic Origin" category, with proportionately more
single-race White grandparents responsible for their grandchildren shown
in the ACS than in Census 2000. This is the same pattern found in Table
3 when comparing the characteristics of all grandparents. No statistical
differences were found between the ACS and Census 2000 percent
distributions by the sex of the grandparent or their poverty status.

# SUMMARY 

Data from the 2004 American Community Survey (ACS) on fertility and
grandparents are consistent with those from the 2004 June Fertility
Supplement to the Current Population Survey (CPS), the Census 2000
Supplementary Survey (C2SS), and Census 2000. The principal difference
noted in this paper for fertility data is the higher proportion of women
with recent births in the ACS than in the CPS who are in population
groups associated with older ages. Data from the ACS for the number of
women with births in the last 12 months came closer to annual birth
levels reported by the National Center for Health Statistics than did
data from the Current Population Survey, even after accounting for
differences in data collection procedures. For grandparent data, the
principal difference noted is the higher proportion of single-race White
grandparents in the ACS than in Census 2000.

[^1]: For a detailed explanation of the basic monthly survey CPS
    sampling frame, see the following Internet site:
    \<[www.bls.census.gov/cps/bsampdes.htm](http://www.bls.census.gov/cps/bsampdes.htm)\>.

[^2]: For a detailed explanation of the Census 2000 sampling frame and
    data collection procedures, see U.S. Census Bureau*, Census 2000
    Summary File 3: Technical Documentation.* U.S. Census Bureau:
    Washington, DC 2002, chapter 8.

[^3]: For a detailed explanation of the C2SS survey and comparisons with
    Census 2000 sample items, see U.S. Census Bureau, *Meeting 21^st^
    Century Demographic Data Needs---Implementing the American Community
    Survey. Report 9: Comparing Social Characteristics with Census
    2000.* Washington, DC, 2004.

[^4]: Deborah Griffin, Susan Love, and Sally Obenski, "Can the American
    Community Survey Replace the Census Long Form?" Paper presented at
    the Annual Meeting of the American Association for Public Opinion
    Research, Nashville, TN, May 14-18, 2003.

[^5]: Responses were given an answer based on household data (assigned)
    rather than a randomly imputed answer (allocated).

[^6]: See the historical table on the annual estimate of births from the
    CPS and the vital statistics system at the Census Bureau webpage
    \<www.census.gov/population/socdemo/fertility/tabM1.csv\>

[^7]: See the 2003 and 2004 reports on births published in *National
    Vital Statistics Reports,* Vol. 54, Nos. 2 and 8 (Hyattsville, MD:
    National Center for Health Statistics, 2005).

[^8]: For a more detailed discussion of race definitions used in the ACS
    see the report "American Community Survey 2004 Subject Definitions"
    (Revised January 2006)

    [www.census.gov/acs/www/Downloads/2004/usedata/Subject_Definitions.pdf](http://www.census.gov/acs/www/Downloads/2004/usedata/Subject_Definitions.pdf)

    For race definitions used in the CPS see Jane Lawler Dye, "Fertility
    of American Women: June 2004," [Current Population
    Reports]{.underline}, P20-555. U.S. Census Bureau, Washington, DC,
    2005.

[^9]: Comparisons by race between the ACS and Census 2000 data should be
    treated with caution because of potential differences in editing
    routines used by the two surveys.