For the last six years, the Reagan administration took pride in rising' incomes and falling unemployment after the deep recession of the early 1980s.</br></br>But at the same time, the ga[ between the richest and the pooresi was getting larger, and the fahiilie: at the bottom suffered an absolute decline in real purchasing power.</br></br>HereÛªs how the numbers behind this paradox shape up, as reported in a study by the House Ways and Means Committee. Average household income, ns measured in constant after-inflation dollars, rose from $27,568 in 1973 to $27,917 in 1979 and $29,487 in 1987ÛÓcomparable high-prosperity years in the business cycle. Unemployment dropped to 5.1 percent, the lowest figure since the early 1970s.</br></br>Adjusted for family size and economies of scale, the committee calculated that the average income of Americans rose by 17.2 percent from 1973 to 1987, .-is measured by after-inflation 1987 dollars.</br></br>But the calculations clearly show that for the one-fifth of households at the bottom of society, average cash income in constant after-inflation dollars dropped from $5,507 in 1973 to $5,107 in 1987ÛÓeven as the top fifth rose from $60,299 to $68,775.