Common Errors in Statistics (and How to Avoid Them), 4th Edition

AGGREGATING DATA

Just as the devil often quotes scripture for his (or her) own purposes, politicians and government agencies are fond of using statistics to mislead. One of the most common techniques is to combine data from disparate sources. Four of the six errors reported by Wise [2005] in the presentation of farm statistics arise in this fashion. (The other two come from employing arithmetic means rather than medians in characterizing highly skewed income distributions.) These errors are:

1. Including “Rural Residence Farms,” which represent two-thirds of all U.S. farms but are not farmed for a living, in the totals for the farm sector. As Wise notes, “This leads to the misleading statement that a minority of farms get farm payments. A minority of part-time farmers get payments, but a significant majority of full-time commercial and family farmers receive farm payments.”

2. Including income from nonfarming activities in farm income.

3. Attributing income to farmers that actually goes to land owners.

4. Mixing data from corporate farms with that of multimember collective entities such as Indian tribes and cooperatives.