As part of the March 1979 Current Population Survey, the Bureau of the Census conducted an experiment in an effort to improve the reporting of income. For the purpose of the experiment, the full CPS sample was divided into two samples—each representative of the U.S. population. An experimental questionnaire was used for one sample consisting of three-eighths of the full sample, and the traditional questionnaire was used for the remaining five-eighths of the full sample. In this text, the income and poverty estimates cited for 1978 are based on the full sample. In addition, the full sample for 1978 was also used to measure changes from 1977, except for women with income, as described below. A discussion of the experiment and its impact on 1978 income and poverty data is provided in a later section entitled, "The March 1979 CPS Income Experiment."

The median income of all families in the United States was $17,640 in 1978, according to results of the Current Population Survey (CPS) conducted in March 1979 by the Bureau of the Census. In 1978, median family income was 10 percent higher than the 1977 median ($16,010). After adjusting for the 7.6-percent increase in prices between 1977 and 1978,¹ there was an increase in real median income of $410 (or 2 percent) for that period. The survey also indicated that there were about 24.5 million persons below the poverty level in 1978 comprising 11.4 percent of the U.S. population.² The size of the poverty population did not change significantly from the 1977 level. The poverty threshold for a nonfarm family of four was $6,662 in 1978.

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¹ The percentage increase in prices between 1977 and 1978 is computed by dividing the annual average Consumer Price Index (CPI) for 1978 by the annual average value of the CPI for 1977.
² See appendix A for an explanation of the poverty concept.