Income inequality perception
If you ask people in the US to estimate the income of someone at the 80th percentile, they underestimate it, thus underestimating income inequality (PDF).
However, if you specify a dollar amount and ask how many people have income above that amount, you get an underestimate of high incomes.
The take-home message? It’s hard to design good survey questions.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »