Interesting. While I agree the results are likely to be inaccurate, this case study targets only the three largest cities in the US. Urban centers probably aren't the best population from which to sample.

In a case like this, we'd probably want to use locations based on number of home sales; and even then, we'd need to account for the amount of time between homes changing hands i/e houses that are flipped. There's likely something to be said about the difference between the nation's average sale price and each area's average sale price; assuming that may affect Zillow's estimations.

Anyways, I like that you're doing studies like this, regardless.