Florida County Data Set. Examine the Florida County data set, described in Appendix C.4. Divide the counties into four groups according to the quartile of their percentage of adults lacking a high school degree. (This quartile information is already part of the data set.)

Do the groups differ significantlywith respect to their median income? In particular, is there a significant linear trend inmedian income? This data is observational.

What limitations does that place on your interpretation? This data is also aggregated.

Using a Web search, what is aggregation bias and how might that further limit your interpretation?

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