This includes the income of the householder and all other individuals 15 years old and over in the household, whether they are related to the householder or not. Because many households consist of only one person, average household income is usually less than average family income. Although the household income statistics cover calendar year 1999, the characteristics of individuals and the composition of households refer to the time of enumeration (April 1, 2000). Thus, the income of the household does not include amounts received by individuals who were members of the household during all or part of calendar year 1999 if these individuals no longer resided in the household at the time of enumeration. Similarly, income amounts reported by individuals who did not reside in the household during 1999 but who were members of the household at the time of enumeration are included. However, the composition of most households was the same during 1999 as at the time of enumeration.

In compiling statistics on family income, the incomes of all members 15 years old and over related to the householder are summed and treated as a single amount. Although the family income statistics cover calendar year 1999, the characteristics of individuals and the composition of families refer to the time of enumeration (April 1, 2000). Thus, the income of the family does not include amounts received by individuals who were members of the family during all or part of calendar year 1999 if these individuals no longer resided with the family at the time of enumeration. Similarly, income amounts reported by individuals who did not reside with the family during 1999 but who were members of the family at the time of enumeration are included. However, the composition of most families was the same during 1999 as at the time of enumeration.

Income for individuals is obtained by summing the eight types of income for each person 15 years old and over. The characteristics of individuals are based on the time of enumeration (April 1, 2000), even though the amounts are for calendar year 1999.

The median divides the income distribution into two equal parts: one-half of the cases falling below the median income and one-half above the median. For households and families, the median income is based on the distribution of the total number of households and families including those with no income. The median income for individuals is based on individuals 15 years old and over with income. Median income for households, families, and individuals is computed on the basis of a standard distribution (see the "Standard Distributions" section under "Derived Measures"). Median income is rounded to the nearest whole dollar. Median income figures are calculated using linear interpolation if the width of the interval containing the estimate is $2,500 or less. If the width of the interval containing the estimate is greater than $2,500, Pareto interpolation is used. (For more information on medians and interpolation, see "Derived Measures".)

Aggregate income is the sum of all incomes for a particular universe. Aggregate income is subject to rounding, which means that all cells in a matrix are rounded to the nearest hundred dollars. (For more information, see "Aggregate" under "Derived Measures".)

Mean income is the amount obtained by dividing the aggregate income of a particular statistical universe by the number of units in that universe. Thus, mean household income is obtained by dividing total household income by the total number of households. (The aggregate used to calculate mean income is rounded. For more information, see "Aggregate income.")

For the various types of income, the means are based on households having those types of income. For households and families, the mean income is based on the distribution of the total number of households and families including those with no income. The mean income for individuals is based on individuals 15 years old and over with income. Mean income is rounded to the nearest whole dollar.

Care should be exercised in using and interpreting mean income values for small subgroups of the population. Because the mean is influenced strongly by extreme values in the distribution, it is especially susceptible to the effects of sampling variability, misreporting, and processing errors. The median, which is not affected by extreme values, is, therefore, a better measure than the mean when the population base is small. The mean, nevertheless, is shown in some data products for most small subgroups because, when weighted according to the number of cases, the means can be added to obtained summary measures for areas and groups other than those shown in census tabulations. (For more information on means, see "Derived Measures".)

Earnings are defined as the sum of wage or salary income and net income from self-employment. "Earnings" represent the amount of income received regularly for people 16 years old and over before deductions for personal income taxes, social security, bond purchases, union dues, medicare deductions, etc.

The median divides the earnings distribution into two equal parts: one-half of the cases falling below the median earnings and one-half above the median. Median earnings is restricted to individuals 16 years old and over and is computed on the basis of a standard distribution (see the "Standard Distributions" section under "Derived Measures"). Median earnings figures are calculated using linear interpolation if the width of the interval containing the estimate is $2,500 or less. If the width of the interval containing the estimate is greater than $2,500, Pareto interpolation is used. (For more information on medians and interpolation, see Derived Measures.)

Aggregate earnings are the sum of wage/salary and net self-employment income for a particular universe of people 16 years old and over. Aggregate earnings are subject to rounding, which means that all cells in a matrix are rounded to the nearest hundred dollars. (For more information, see "Aggregate" under "Derived Measures".)

Mean earnings is calculated by dividing aggregate earnings by the population 16 years old and over with earnings. (The aggregate used to calculate mean earnings is rounded. For more information, see "Aggregate earnings.") Mean earnings is rounded to the nearest whole dollar. (For more information on means, see "Derived Measures".)

Per capita income is the mean income computed for every man, woman, and child in a particular group. It is derived by dividing the total income of a particular group by the total population in that group. (The aggregate used to calculate per capita income is rounded. For more information, see "Aggregate" under "Derived Measures".) Per capita income is rounded to the nearest whole dollar. (For more information on means, see "Derived Measures".)

Since answers to income questions are frequently based on memory and not on records, many people tended to forget minor or sporadic sources of income and, therefore, underreport their income. Underreporting tends to be more pronounced for income sources that are not derived from earnings, such as public assistance, interest, dividends, and net rental income.

Extensive computer editing procedures were instituted in the data processing operation to reduce some of these reporting errors and to improve the accuracy of the income data. These procedures corrected various reporting deficiencies and improved the consistency of reported income items associated with work experience and information on occupation and class of worker. For example, if people reported they were self employed on their own farm, not incorporated, but had reported wage and salary earnings only, the latter amount was shifted to self-employment income. Also, if any respondent reported total income only, the amount was generally assigned to one of the types of income items according to responses to the work experience and class-of-worker questions. Another type of problem involved nonreporting of income data. Where income information was not reported, procedures were devised to impute appropriate values with either no income or positive or negative dollar amounts for the missing entries. (For more information on imputation, see "Accuracy of the Data.")

In income tabulations for households and families, the lowest income group (for example, less than $10,000) includes units that were classified as having no 1999 income. Many of these were living on income "in kind," savings, or gifts, were newly created families, or were families in which the sole breadwinner had recently died or left the household. However, many of the households and families who reported no income probably had some money income that was not reported in the census.

The income data collected in the 1970, 1980, and 1990 censuses are similar to Census 2000 data, but there are variations in the detail of the questions. In 1990, income information for 1989 was collected from people in approximately 17 percent of all housing units and group quarters. Each person 15 years old and over was required to report:

• Wage or salary income
• Net nonfarm self-employment income
• Net farm self-employment income
• Interest, dividend, or net rental or royalty income
• Social security or railroad retirement income
• Supplemental Security Income (SSI), Aid to Families With Dependent Children (AFDC), or other
• public assistance income
• Retirement, survivor, or disability income
• Income from all other sources

Since the number of respondents reporting farm self-employment income has become smaller over the years, the farm and nonfarm self-employment items were combined into one item for Census 2000. Data users are still able to obtain an estimate of "farm self-employment" income by looking at net self-employment income in combination with other labor force related questions such as "occupation of longest job." Supplemental Security Income (SSI) was asked separately from other public assistance income or welfare received from a state or local welfare office in Census 2000.

Between the 1990 census and Census 2000, there were minor differences in the processing of the data. In both censuses, all people with missing values in one or more of the detailed type of income items were designated as allocated. Each missing entry was imputed either as a "no" or as a dollar amount. If total income was reported and one or more of the type of income fields was not answered, then the entry in total income generally was assigned to one of the income types according to the socioeconomic characteristics of the income recipient. This person was designated as unallocated.

In 2000 and 1990, all nonrespondents with income not reported (whether householders or other people) were assigned the reported income of people with similar characteristics. (For more information on imputation, see "Accuracy of the Data.")

In 1980, income information for 1979 was collected from people in approximately 19 percent of all housing units and group quarters. Each person 15 years old and over was required to report:

• Wage or salary income
• Net nonfarm self-employment income
• Net farm self-employment income
• Interest, dividend, or net rental or royalty income
• Social security or railroad retirement income
• Supplemental Security Income (SSI), Aid to Families With Dependent Children (AFDC), or other public assistance income
• Income from all other sources

There was a difference in the method of computer derivation of aggregate income from individual amounts. In the 1980 census, income amounts less than $100,000 were coded in tens of dollars, and amounts of $100,000 or more were coded in thousands of dollars; $5 was added to each amount coded in tens of dollars and $500 to each amount coded in thousands of dollars. Entries of $999,000 or more were treated as $999,500 and losses of $9,999 or more were treated as minus $9,999. In the 1990 and 2000 censuses, income amounts less than $999,999 were keyed to the nearest dollar. Amounts of $999,999 or more were treated as $999,999 and losses of $9,999 or more were treated as minus $9,999 in all of the computer derivations of aggregate income.

In 1970, information on income in 1969 was obtained from all members in every fifth housing unit 14 years old and over and small group quarters (less than 15 people) and every fifth person in all other group quarters. Each person 14 years old and over was required to report:

• Wage or salary income
• Net nonfarm self-employment income
• Net farm self-employment income
• Social security or railroad retirement income
• Supplemental Security Income (SSI), Aid to Families With Dependent Children (AFDC), or other public assistance income
• Income from all other sources

If a person reported a dollar amount in wage or salary, net nonfarm self-employment income, or net farm self-employment income, the person was considered as unallocated only if no further dollar amounts were imputed for any additional missing entries.

In 1960, data on income were obtained from all members 14 years old and over in every fourth housing unit and from every fourth person 14 years old and over living in group quarters. Each person was required to report wage or salary income, net self-employment income, and income other than earnings received in 1959. An assumption was made in the editing process that no other type of income was received by a person who reported the receipt of either wage and salary income or self-employment but who had failed to report the receipt of other money income.

For several reasons, the income data shown in census tabulations are not directly comparable with those that may be obtained from statistical summaries of income tax returns. Income, as defined for federal tax purposes, differs somewhat from the Census Bureau concept. Moreover, the coverage of income tax statistics is different because of the exemptions of people having small amounts of income and the inclusion of net capital gains in tax returns. Furthermore, members of some families file separate returns and others file joint returns; consequently, the income reporting unit is not consistently either a family or a person.

The earnings data shown in census tabulations are not directly comparable with earnings records of the Social Security Administration. The earnings record data for 1999 excluded the earnings of some civilian government employees, some employees of nonprofit organizations, workers covered by the Railroad Retirement Act, and people not covered by the program because of insufficient earnings. Because census data are obtained from household questionnaires, they may differ from Social Security Administration earnings record data, which are based upon employers reports and the federal income tax returns of self-employed people.

The Bureau of Economic Analysis (BEA) of the Department of Commerce publishes annual data on aggregate and per-capita personal income received by the population for states, metropolitan areas, and selected counties. Aggregate income estimates based on the income statistics shown in census products usually would be less than those shown in the BEA income series for several reasons. The Census Bureau data are obtained directly from households; whereas, the BEA income series is estimated largely on the basis of data from administrative records of business and governmental sources. Moreover, the definitions of income are different. The BEA income series includes some items not included in the income data shown in census publications, such as income "in kind," income received by nonprofit institutions, the value of services of banks and other financial intermediaries rendered to people without the assessment of specific charges, medicare payments, and the income of people who died or emigrated prior to April 1, 2000. On the other hand, the census income data include contributions for support received from people not residing in the same household if the income is received on a regular basis.

In comparing income data for 1999 with earlier years, it should be noted that an increase or decrease in money income does not necessarily represent a comparable change in real income, unless adjustments for changes in prices are made.

Even though the official poverty data are based on the 48 thresholds arranged by family size and number of children within the family, data users often want to get an idea of the "average" threshold for a given family size. The weighted average thresholds provide that summary. They are weighted averages because for any given family size, families with a certain number of children may be more or less common than families with a different number of children. In other words, among 3-person families, there are more families with two adults and one child than families with three adults. To get the weighted average threshold for families of a particular size, multiply each threshold by the number of families for whom that threshold applies; then add up those products, and divide by the total number of families who are of that family size.

For example, for 3-person families, 1999 weighted thresholds were calculated in the following way using information from the 2000 Current Population Survey:

Family type	Number of families	Threshold
No children (three adults)	5,213	*	$13,032	=	$67,935,816
One child (two adults)	8,208	*	$13,410	=	$110,069,280
Two children (one adult)	2,656	*	$13,423	=	$35,651,488
Totals	16,077				$213,656,584
Source: Current Population Survey, March 2000.

Dividing $213,656,584 by 16,077 (the total number of 3-person families) yields $13,290, the weighted average threshold for 3-person families. Please note that the thresholds are weighted not just by the number of poor families, but by all families for which the thresholds apply: the thresholds are used to determine which families are at or above poverty, as well as below poverty.

Poverty status was determined for all people except institutionalized people, people in military group quarters, people in college dormitories, and unrelated individuals under 15 years old. These groups also were excluded from the numerator and denominator when calculating poverty rates. They are considered neither "poor" nor "nonpoor."

For various reasons, the official poverty definition does not satisfy all the needs of data users. Therefore, some of the data reflect the number of people below different percentages of the poverty level. These specified poverty levels are obtained by multiplying the official thresholds by the appropriate factor. For example, the average income cutoff at 125 percent of the poverty level was $21,286 ($17,029 x 1.25) in 1999 for family of four people.

Poverty Threshold in 1999, by Size of Family and Number of Related Children Under 18 Years Old (Dollars)
Size of family unit	Weighted average threshold	Related children under 18 years old
		None	One	Two	Three	Four	Five	Six	Seven	Eight or more
One person (unrelated individual)	8501
Under 65 years old	8667	8667
65 years old and over	7990	7990
Two people	10869
Householder under 65 years old	11214	11156	11483
Householder 65 years old and over	10075	10070	11440
Three people	13290	13032	13410	13423
Four people	17029	17184	17465	16895	16954
Five people	20127	20723	21024	20380	19882	19578
Six people	22727	23835	23930	23436	22964	22261	21845
Seven people	25912	27425	27596	27006	26595	25828	24934	23953
Eight people	28967	30673	30944	30387	29899	29206	28327	27412	27180
Nine people or more	34417	36897	37076	36583	36169	35489	34554	33708	33499	32208

Income deficit represents the difference between the total income of families and unrelated individuals below the poverty level and their respective poverty thresholds. In computing the income deficit, families reporting a net income loss are assigned zero dollars and for such cases the deficit is equal to the poverty threshold. This measure provides an estimate of the amount which would be required to raise the incomes of all poor families and unrelated individuals to their respective poverty thresholds. The income deficit is thus a measure of the degree of the impoverishment of a family or unrelated individual. However, please use caution when comparing the average deficits of families with different characteristics. Apparent differences in average income deficits may, to some extent, be a function of differences in family size.

Aggregate income deficit refers only to those families or unrelated individuals who are classified as below the poverty level. It is defined as the group (e.g., type of family) sum total of differences between the appropriate threshold and total family income or total personal income. Aggregate income deficit is subject to rounding, which means that all cells in a matrix are rounded to the nearest hundred dollars. (For more information, see "Aggregate" under "Derived Measures".)

Mean income deficit represents the amount obtained by dividing the total income deficit for a group below the poverty level by the number of families (or unrelated individuals) in that group. (The aggregate used to calculate mean income deficit is rounded. For more information, see "Aggregate income deficit.") As mentioned above, please use caution when comparing mean income deficits of families with different characteristics, as apparent differences may to some extent be a function of differences in family size. Mean income deficit is rounded to the nearest whole dollar. (For more information on means, see "Derived Measures".)

The poverty definition used in the 1980 census and later differed slightly from the one used in the 1970 census. Three technical modifications were made to the definition used in the 1970 census:

1. Beginning with the 1980 census, the Office of Management and Budget eliminated any distinction between thresholds for "families with a female householder with no husband present" and all other families. The new thresholds - which apply to all families regardless of the householder's sex - were a weighted average of the old thresholds.

2. The Office of Management and Budget eliminated any differences between farm families and nonfarm families, and farm and nonfarm unrelated individuals. In the 1970 census, the farm thresholds were 85 percent of those for nonfarm families; whereas, in 1980 and later, the same thresholds were applied to all families and unrelated individuals regardless of residence.

3. The thresholds by size of family were extended from seven or more people in 1970 to nine or more people in 1980 and later.

These changes resulted in a minimal increase in the number of poor at the national level. For a complete discussion of these modifications and their impact, see U.S. Census Bureau, Current Population Reports, " Characteristics of the Population Below the Poverty Level: 1980," P-60, No. 133.

With respect to poverty, the population covered in the 1970 census was almost the same as that covered in the 1980 census and later. The only difference was that in 1980 and after, unrelated individuals under 15 years old were excluded from the poverty universe, while in 1970, only those under age 14 were excluded. The limited poverty data from the 1960 census excluded all people in group quarters and included all unrelated individuals regardless of age. It was unlikely that these differences in population coverage would have had significant impact when comparing the poverty data for people since the 1960 census.

Because the questionnaires and data collection procedures differ, Census 2000 estimates of the number of people below the poverty level by various characteristics may differ from those reported in the March 2000 Current Population Survey. Please refer to www.census.gov/hhes/income/guidance.htmlfor more details.

Poverty status is not defined for households - only for families and unrelated individuals. Because some data users need poverty data at the household level, we have provided a few matrices that show tallies of households by the poverty status of the householder. In these matrices, the householder's poverty status is computed exactly the same way as described above. Therefore, to determine whether or not a "household" was in poverty, anyone who is not related to the householder is ignored.

Example #1: Household #1 has six members - a married couple, Alice and Albert, with their 10-year-old nephew, Aaron, and another married couple, Brian and Beatrice, with their 6-year-old son, Ben. Alice is the householder. Brian, Beatrice, and Ben are not related to Alice.

Household member	Relationship to Alice	Income
Alice	self (householder)	$5,000
Albert	spouse	$40,000
Aaron	related child	$0
Brian	unrelated individual	$0
Beatrice	unrelated individual	$5,000
Ben	unrelated individual	$0

The total income of Alice's family is $45,000, and their poverty threshold is $13,410, since there are three people in the family, with one member under age 18. Their income is greater than their threshold, so they are not classified as poor. Their ratio of income to poverty is 3.36 ($45,000 divided by $13,410). Alice's income-to-poverty ratio is also 3.36, because everyone in the same family has the same poverty status.
Even though Brian, Beatrice and Ben would be classified as poor if they lived in their own household, the household is not classified as poor because the householder, Alice, is not poor, as was shown in the computation above.

Example #2: Household #2 consists of four adults, Claude, Danielle, Emily, and Francis, who are unrelated to each other and are living as housemates. Claude, who is age 30, is the householder.

Household member	Relationship to Claude	Income
Claude	self (householder)	$4,500
Danielle	unrelated individual	$82,000
Emily	unrelated individual	$28,000
Francis	unrelated individual	$40,000

Because Claude is under age 65 and is not living with any family members, his poverty threshold is $8,667. Since his income, $4,500, is less than his threshold, he is considered poor. His ratio of income to poverty is 0.52 ($4,500 divided by $8,667).
Household #2 would be classified as poor because its householder, Claude, is poor, even though the other household members (who are not related to Claude) are not in poverty.