The Insidious Assumptions We Make

I was often laughed at when I worked for ASCS because to create example cases of how the farm program would work, I always used 100 acres of corn with 100 bushel yield.  Made it much easier to calculate.  It also was unrealistic even in 1980, and would be ridiculous today.  And I vaguely remember the symmetry of numbers leading to a screwup--something which seemed reasonable with the assumed numbers wasn't.

That's the case with Megan McArdle's recent post on savings. She writes;

 Say you're a 40 year old couple with 100,000 a year in after-tax income, and you save 5% of that, the way ordinary Americans do.  (Assume further that it all goes in retirement).

My point? A couple with $100,000 after tax income is earning maybe $120,000 or more in before tax income. Such a couple is probably close to being in the top 10 percent of the US households, i.e., not "ordinary" and not a good example to use for a discussion of savings.