In 1970 the median income in the United States was $56,000 per year, and in 2017 the median income was $68,000 per year (see Fig. 1, top curve). In 1970 the median cost of a three-bedroom family home was $23,400, and in 2017 the median cost of such a home was $325,000 (Norada Real Estate 2025; FedPrimeRate.com 2025). Thus in 1970 an individual would need to work 0.4 years to afford such a home (i.e., $23,400/$56,000 per year), and in 2017 an individual would need to work 4.8 years to afford such a home (i.e., $325,000/$68,000 per year), some 12 times longer. Moreover, this diminished relative income of the middle class is depicted by an increase in the Gini coefficient between 1970 and 2017 (Fig. 1, bottom curve).
The income distribution is not a normal function but rather a lognormal function, since it is limited by zero income (see Fig. 2). This means that when evaluating the income distribution, one cannot rely on the mean, given that the mean is biased toward the high-income earners. In fact, the median value of a lognormal distribution can be used to evaluate the income disparity of a population by noting the discrepancy between the median value (below which represents half the population) and the mean value (below which represents more than half the population). The ratio between the mean and the medium is another way of assessing income inequality (Schield 2018).
Note, both the income distribution and the Gini coefficient do not factor in acquired wealth through capital gains. Such information is proprietary and therefore it is not made available to the public by the Internal Revenue Service, which puts limits on the precision of estimates on income distribution (Schield 2018). This rule needs to be made conditional for the purpose of managing economic incentives, since all members of society (including the wealthy) benefit from the deployment of government funds toward infrastructure, science, and technology through agencies such as DOT, DOE, EPA, USDA, HUD, FEMA, DARPA, NSF, NIH, and so on.
Figure 1: Median income (top curve) and Gini coefficient values (bottom curve) are plotted from 1968 to 2017 for US households. Data from figure 8 of Schield (2018). (file: bible_009.jpg)
Figure 2: Frequency plot of number of households and household pre-tax income. Data from figure 1 of Schield (2018). For other details see Schield (2018). (file: bible_010.jpg)