I'm not an economist, but this seems like a strange index. Is job quality really binary? Are pay and hours sufficient to make a binary determination? Without a

I'm not an economist, but this seems like a strange index. Is job quality really binary? Are pay and hours sufficient to make a binary determination? Without analyzing the data, it seems like a proxy for income inequality. If salaries go up for top earners, but stay stagnant for everyone else, then more people have a "below average" income, even if their hours and pay are unchanged.