You need it to be "Also, income inequality, measured by the ratio of the average income of the top 10% of wage earners compared to the bottom 90%"
But the linked article doesn't make sense either, or maybe I'm just not getting it. It put it this way: "Under President Hoover, income inequality, as measured by the ratio of the average income of the top 10 percent compared to the average income of the bottom 90 percent, rose from 7.1 percent in 1929 to 7.8 percent in 1932."
Ratios are when you compare two quantities, like 1:9. Percentages are fractions of a whole. So it's strange to express a ratio as a percentage. The obvious interpretation is to say that a ratio of 7% means a ratio of 7:93. But I don't think that's what they're saying, because in the same paragraph they say:
"These periods of high-income inequality sharply contrast the period 1942–1987, when the ratio of top incomes to the incomes of most Americans never exceeded five."
Which would imply a percentage of 17%, if we're using this strange ratio/percentage conversion. That is: 17:73, i.e. 1:5. But they seem to think that higher is worse, so that can't be it.
Maybe they never meant to put percentage symbols in there, and they just meant that the average income of the top 10% is 7.9 times higher than the bottom 90%. If that's the case, I would distrust that source if I were you. That's a basic error.