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-eights 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."

In 1978 the median family income was $17,640, 10 percent over the 1977 median of $16,010. After adjusting for the 7.6-percent increase in prices between 1977 and 1978,¹ the median family income in terms of constant dollars increased by $410 or about 2 percent. Unrelated individuals had a median income of $6,710 in 1978, about 5 percent (or $350) higher in real terms than the 1977 median.

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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.