Generally when you want to discuss income breakdowns in scientific terms you use income Quartiles (or quintiles, etc). By defining locality and timeframe (top

Generally when you want to discuss income breakdowns in scientific terms you use income Quartiles (or quintiles, etc). By defining locality and timeframe (top quintile of americans? californians? residents of 90210? in 1990? 2008?) you can easily scale in a way that people still understand. People have strongly differing concepts of class, whereas (most) everyone knows what the lowest 25% of earners look like in thier community. The concepts are still valid, it's just a matter of narrowing the terms. Edit: If you're discussing income in many countries (esp the US) it may be wise to split off the top 1% or 0.5%, as they tend to make so much that it strongly influences the averages.