Appendix 2: Methodology
Demographic Analysis Data Sources
The demographic data in this report are derived from the Current Population Survey, which covers the civilian, noninstitutional population. Unless otherwise noted, all data come from the CPS Annual Social and Economic Supplements (ASEC) conducted in March of every year. Unless otherwise noted, the specific files used in this report are from March 2012, the latest year for which ASEC data are available. Conducted jointly by the U.S. Census Bureau and the Bureau of Labor Statistics, the CPS is a monthly survey of approximately 55,000 households and is the source of the nation’s official statistics on unemployment. The ASEC survey in March features a larger sample size as well as an expanded set of detailed questions, and it provides an update of the nation’s social and economic portrait each year. Data on income and poverty from the ASEC survey serves as the basis for the well-known Census Bureau report on income, poverty and health insurance in the United States (DeNavas-Walt, Proctor and Smith, 2011). The ASEC surveys also collect data on the income of a household in the preceding calendar year. Thus, the 2012 file used in this report contains data on income from 2011.
Data on voting and turnout come from the November 2010 Voting and Registration Supplement of the CPS. Data on fertility, as stated below, come from multiple years of a June supplement to the CPS.
The CPS microdata used in this report are the Integrated Public Use Microdata Series (IPUMS) provided by the University of Minnesota. The IPUMS assigns uniform codes, to the extent possible, to data collected in the CPS over the years. More information about the IPUMS, including variable definition and sampling error, is available at http://cps.ipums.org/cps/documentation.shtml.
Intermarriage rates in this report were estimated for all married adults living with their spouse, whose marital status in the survey data is “married, spouse present.” The unit of analysis in this section of the report is married adults. The IPUMS database includes linkages of spouse records and supplies “attached variables” that place the value for the spouse’s variable on each record. Thus, the first step of analysis was to attach the race, ethnicity and nativity of the spouse to the individual’s record. The second step was to generate variables for the race and ethnic origin of the individual and his or her spouse. Seven different groups were constructed for estimating intermarriage rates: Hispanic and six non-Hispanic racial groups—white alone, black alone, Asian alone, American Indian and Alaska Native alone, Native Hawaiian and Pacific Islander alone, and more than one race. This report includes two different intermarriage rates—race-ethnicity and nativity. For race-ethnicity, the intermarriage rate is the number of people married to a spouse of a different race-ethnic group divided by the number of married people. For nativity, the intermarriage rate is the number of natives with foreign-born spouses (and immigrants with native spouses) divided by the total married population.
Dependent children refers to children of the household head who are younger than 18, or ages 18-24 and economically dependent. Economic dependency was established as follows:
- 18-21 and enrolled in high school full time
- 18-24 and enrolled in college full time with part-time job
- 18-24 and enrolled in high school or college part time with part-time job and income less than 50% of the individual poverty level
- 18-24 with part-time job and income less than 50% of the individual poverty level
- 18-24 with full-time job and no income
Household income is the sum of incomes earned by all members of the household in the calendar year preceding the date of the survey. The CPS collects data on money income received (exclusive of certain money receipts, such as capital gains) before payments for such things as personal income taxes, Social Security, union dues and Medicare deductions. Non-cash transfers, such as food stamps, health benefits, subsidized housing and energy assistance, are not included. The Census Bureau also states that “… there is a tendency in household surveys for respondents to under report their income. From an analysis of independently derived income estimates, it has been determined that wages and salaries tend to be much better reported than such income types as public assistance, Social Security, and net income from interest, dividends, rents, etc.” More detail on the definition of income in the CPS is available in the documentation of the data (http://www.census.gov/apsd/techdoc/cps/cpsmar11.pdf). It should be noted that income data in the CPS public-use microdata files are top coded to prevent the identification of a few individuals who might report very high levels of income.
Adjusting Income for Household Size
Household income data reported in this study are adjusted for the number of people in a household. That is done because a four-person household with an income of, say, $50,000 faces a tighter budget constraint than a two-person household with the same income. In addition to comparisons across households at a given point in time, this adjustment is useful for measuring changes in the income of households over time. That is because average household size in the United States has decreased from 3.2 persons in 1970 to 2.5 persons in 2010, a drop of about 20%. Ignoring this demographic change would mean ignoring a commensurate loosening of the household budget constraint.
At its simplest, adjusting for household size could mean converting household income into per capita income. Thus, a two-person household with an income of $50,000 would have a per capita income of $25,000, double the per capita income of a four-person household with the same total income.
A more sophisticated framework for household size adjustment recognizes that there are economies of scale in consumer expenditures. For example, a two-bedroom apartment may not cost twice as much to rent as a one-bedroom apartment. Two household members could carpool to work for the same cost as a single household member, and so on. For that reason, most researchers make adjustments for household size using the method of “equivalence scales” (Garner, Ruiz-Castillo and Sastre, 2003, and Short, Garner, Johnson and Doyle, 1999).
A common equivalence-scale adjustment is defined as follows:
Adjusted household income = Household income / (Household size)N
By this method, household income is divided by household size exponentiated by “N,” where N is a number between 0 and 1.
Note that if N = 0, the denominator equals 1. In that case, no adjustment is made for household size. If N = 1, the denominator equals household size, and that is the same as converting household income into per capita income. The usual approach is to let N be some number between 0 and 1. Following other researchers, this study uses N = 0.5 (for example, see Johnson, Smeeding and Torrey, 2005). In practical terms, this means that household income is divided by the square root of household size—1.41 for a two-person household, 1.73 for a three-person household, 2.00 for a four-person household, and so on.36
Once household incomes have been converted to a “uniform” household size, they can be scaled to reflect any household size. The income data reported in this study are computed for three-person households, the closest whole number to the average size of a U.S. household since 1970. That is done as follows:
Three-person household income = Adjusted household income * [(3)0.5]
As discussed in the main body of the report, adjusting for household size has an effect on trends in income since 1970. However, it is important to note that once the adjustment has been made, it is immaterial whether one scales incomes to one-, two-, three- or four-person households. Regardless of the choice of household size, the same results would emerge with respect to the trends in the well-being of lower-, middle- and upper-income groups.
Fertility data are derived from the June supplement of the CPS, which includes fertility information from female respondents ages 15 to 44. Any woman who gave birth from the prior June through the month of May preceding the survey is included, and the mother’s characteristics are based upon the information provided at the time of the survey.
In order to increase sample size, the analyses are based upon an aggregation of 2004, 2006, 2008 and 2010 data (the June supplement is administered only in even-numbered years). Even with the data aggregation, cell sizes were too small to estimate the share of women who were unmarried when they gave birth for first- and second-generation black women, and for second-generation Asian-American women.
All variables are based upon the characteristics of the mother, not of the father or the baby. A mother is described as married if she is either married or separated at the time of the survey. Otherwise she is considered unmarried.
The nation’s official birth data from the National Center for Health Statistics (NCHS) include a record for each baby born, while the CPS data account for each mother giving birth. Given that approximately 3% of live births include multiples (twins, triplets, etc.), the CPS slightly undercounts the number of babies born. In NCHS data, marital status refers to the mother’s marital status at the time of the birth.
Estimates of multi-generational households are based on definitions similar to those in previous Pew Research Center reports about such households, including Kochhar and Cohn (2011).
Voting Eligibility and Behavior
Electoral data are derived from the November 2010 Voting and Registration Supplement of the CPS, which includes questions regarding voting registration and voting behavior in past elections. Voting eligibility is based on adulthood (age 18 or older) and citizenship.
Data presented in this report on projected populations through 2050 are consistent with projections published in Passel and Cohn (2008). These projections include subdivisions of the population by race-Hispanic origin and generation.
Historical Data on Generations
The information required to define the first, second and third generations—nativity, citizenship, and country of birth of parents—was not collected consistently in our primary sources of historical demographic data, the U.S. censuses. The questions on country of birth of parents were dropped from the census beginning in 1980, and citizenship information has been inconsistently collected in 20th-century censuses. Moreover, the information across censuses has not always been consistent with trends in immigration or other censuses. To fill this gap, Passel and Cohn (2008) presented historical reconstructions of race-generation data for 1960-2000 based on the population projection methodology used for 2005-2050. Edmonston and Passel (1994) used similar methods to trace the generational composition of race-Hispanic groups back to 1900. These two historical reconstructions are the basis for trends in generational composition presented in this report for 1900-2000.
Historical Data on Immigration Waves
During the first two waves of immigration described here, 1840-1889 and 1890-1919, virtually all immigrants who arrived in the United States did so legally and were processed and counted by immigration authorities. Historical data on legal immigrants arriving are presented annually in the Yearbook of Immigration Statistics, released by the Department of Homeland Security (DHS). Table 2 of the Yearbook shows immigrants arriving by country or region of birth for each decade from 1820 to the present and is the source for our information.
For the most recent wave of immigration from 1965 to the present, data on legal admissions are insufficient because a significant amount of immigration has been unauthorized and because the official data count immigrants when they are admitted legally, not when they arrive. Data from decennial censuses since 1980 and from the American Community Survey (ACS) include most of the unauthorized immigrants and, thus, provides a better count of the total number of immigrants. Because many immigrants come to the U.S. and subsequently leave (or die), the best census or survey estimating the number of arriving immigrants during a period is one close to that period; for example, using the 2011 ACS to estimate the number of immigrants who arrived during the 1970s would seriously understate the number of immigrants. Accordingly, the estimates presented in this report use a number of sources to estimate the magnitude of immigration. For 1965-1980, the counts of immigrants come from the foreign-born population enumerated in the 1980 Census who reported arriving in 1965 or later; for 1980-1990, estimates come from the 1990 Census; and for 1990-1999, the estimates come from the 2000 Census. Tabulations used in this report come from the 5% IPUMS samples of these three decennial censuses. After 2000, the ACS is the source for this information. For immigrants arriving in 2000-2004, estimates come from the 2005 and 2006 ACS. For 2005-2010, the estimates for each individual year come from the next year’s ACS—e.g., the estimate for 2007 comes from the 2008 ACS. Weights for the 2005-2009 ACS were modified to be consistent with results from the 2000 and 2010 Censuses (see Passel and Cohn 2012 for an explanation).
Survey Data Sources
Survey data in this report are based on Pew Research Center surveys. Survey data for Hispanics come from one of two sources: the 2012 or the 2011 National Survey of Latinos. Survey data for Asian Americans come from the 2012 Asian-American Survey. Survey data for the U.S. general public come from a variety of sources; these are listed in the topline results in Appendix 3.
Differences between groups or subgroups, such as first- and second-generation Hispanics or first- and second-generation Asian Americans, are described in this report only when the relationship is statistically significant and therefore unlikely to occur by chance. Statistical tests of significance take into account the complex sampling design used for the surveys and the effect of weighting.
Survey Data: Hispanics
Data from two nationally representative surveys of Hispanics are included in this report.
- The 2012 National Survey of Latinos was conducted with a nationally representative sample of 1,765 Hispanic adults ages 18 and older living in the United States. The survey was conducted Sept. 7-Oct. 4, 2012, in all 50 states and the District of Columbia.
- The 2011 National Survey of Latinos was conducted with a nationally representative sample of 1,220 Hispanic adults ages 18 and older living in the United States. The survey was conducted Nov. 9-Dec. 7, 2011, in all 50 states and the District of Columbia.
Both surveys were conducted in both English and Spanish on cellular as well landline telephones. Interviews were conducted for the Pew Hispanic Center by Social Science Research Solutions (SSRS). The 2012 survey also included an oversample of non-Catholic Hispanics; the results are weighted to account for this oversampling.
For more details on the 2012 National Survey of Latinos see Appendix B in “Latino Voters Support Obama by 3-1 Ratio, But Are Less Certain than Others about Voting.” For more details on the 2011 National Survey of Latinos methodology see Appendix A in “When Labels Don’t Fit: Hispanics and Their Views of Identity,” April 4, 2012.
Survey Data: Asian Americans
The Pew Research Center’s 2012 Asian-American Survey is based on telephone interviews conducted by landline and cell phone with a nationally representative sample of 3,511 Asian adults ages 18 and older living in the United States. The survey was conducted Jan. 3-March 27, 2012, in all 50 states, including Alaska and Hawaii, and the District of Columbia. The survey was conducted using a probability sample from multiple sources. The data are weighted to produce a final sample that is representative of Asian adults in the United States. Survey interviews were conducted under the direction of Abt SRBI, in English and Cantonese, Hindi, Japanese, Korean, Mandarin, Tagalog and Vietnamese.
Respondents who identified as “Asian or Asian American, such as Chinese, Filipino, Indian, Japanese, Korean, or Vietnamese” were eligible to complete the survey interview, including those who identified with more than one race and regardless of Hispanic ethnicity. The question on racial identity also offered the following categories: white, black or African American, American Indian or Alaska Native, and Native Hawaiian or other Pacific Islander.
U.S. Asian groups, subgroups, heritage groups and country-of-origin groups are used interchangeably in this report to reference respondents’ self-classification into “specific Asian groups.” This self-identification may or may not match respondents’ country of birth or their parents’ country of birth. Self-classification is based on responses to an open-ended question asking for a respondent’s “specific Asian group.” Asian groups named in this open-ended question were “Chinese, Filipino, Indian, Japanese, Korean, Vietnamese, or of some other Asian background.” Respondents self-identified with more than 22 specific Asian groups. Those who identified with more than one Asian group were classified based on the group with which “they identify most.” Many questions on the survey used question wording customized to match the respondent’s self-identification into country-of-origin groups. See the topline in Appendix 3 for details on question wording.
For more details on the methodology, see Appendix 1: Survey Methodology in the “The Rise of Asian Americans.”
Survey Data: General Public
Figures for the U.S. general public are based on nationally representative surveys of respondents of any race. See the topline in Appendix 3 for the survey source on a specific question. Details on the methodology of each survey are available at www.pewresearch.org.
Comparisons between the U.S. general public and Hispanics may understate or overstate the magnitude of differences between U.S. Hispanics and Americans who are not Hispanic, due to the fact that Hispanics are also part of the general public to which the comparison is made. The same is true of comparisons between Asian Americans and Americans who are not Asian and of any other subgroup of the U.S. general public. The maximum possible size of such an effect would be equal to the size of the subgroup in the U.S. population. The maximum possible size of such an effect would occur only if responses of the subgroup members and Americans who are not members of the subgroup were completely different on a specific survey question.
DeNavas-Walt, Carmen, Bernadette D. Proctor, and Jessica C. Smith. 2011. “Income, Poverty, and Health Insurance Coverage in the United States: 2010.” Current Population Reports, Consumer Income, P60-239. Washington, DC: U.S. Census Bureau, September.
Edmonston, Barry and Jeffrey S. Passel. 1994. “The Future Immigrant Population of the United States,” Immigration and Ethnicity: The Integration of America’s Newest Arrivals, edited by Barry Edmonston and Jeffrey S. Passel, Washington, DC: The Urban Institute Press.
Garner, Thesia, Javier Ruiz-Castillo, and Mercedes Sastre. 2003. “The Influence of Demographics and Household-Specific Price Indices on Consumption-Based Inequality and Welfare: A Comparison of Spain and the United States.” Southern Economic Journal 70(1): 22-48.
Kochhar, Rakesh and D’Vera Cohn. 2011. “Fighting Poverty in a Bad Economy, Americans Move in with Relatives.” Washington, DC: Pew Social & Demographic Trends project, October 3.
Johnson, David S., Timothy M. Smeeding, and Barbara Boyle Torrey. 2005. “Economic Inequality Through the Prisms of Income and Consumption.” Monthly Labor Review, April: 11-24.
Passel, Jeffrey S. and D’Vera Cohn. 2012. “U.S. Foreign-Born Population: How Much Change from 2009 to 2010?” Washington, DC: Pew Hispanic Center. January 9.
Passel, Jeffrey S. and D’Vera Cohn. 2008. “U.S. Population Projections: 2005-2050.” Washington, DC: Pew Social & Demographic Trends project. February 11.
Short, Kathleen, Thesia Garner, David Johnson, and Patricia Doyle. 1999. “Experimental Poverty Measures: 1990 to 1997.” Current Population Reports, Consumer Income, P60-205. Washington, DC: U.S. Census Bureau, June.
- One issue with adjusting for household size is that while demographic data on household composition pertain to the survey date, income data typically pertain to the preceding year. Because household composition can change over time, for example, through marriage, divorce or death, the household size that is measured at the survey date may not be the same as that at the time the income was earned and spent (Debels and Vandecasteele, 2008). ↩