It's also why I'm a stickler for pointing out that no, 150K is NOT "middle income" or "average."
What Z-score range (how many standard deviations) does your definition of "average" comprise? Is it -1 to 1, -2 to 2, or -0.1 to -0.1? If a gifted program has a an IQ cutoff of 130, and special ed has an IQ cutoff of 70, then students with IQs from 70 to 130, a Z-score range of -2 to 2, are effectively being considered "average" or "normal".
Yes, an income of 150K is above average, but if you group households into the categories of poor, middle class, and rich,
where you set the thresholds is a matter of judgement. How the $150K is earned should also be considered. I consider a
couple each earning $75K more "middle class" than one where the husband earns $150K and the wife can afford to be a SAHM.
