Margin of Error vs. Geography in the ACS

I just wrote a blog post on Margin of Error vs. Geography in the ACS. I'd love feedback from members of this group: www.arilamstein.com/.../
Parents
  • You may want to mention that the main two determinants of the MoE are the sample size, as the square root of the n (lower for a tract than for a county, in most situations), roughly (there are technicalities), and the mean income itself. I think of income as approximately constant coefficient of variation variable. Coefficient of variation = standard deviation in the population / mean. For a ZIP code with mean income of $15K, you can expect the standard deviation to be may be $20K, and for a ZIP code with mean income of $100K, the standard deviation could be $130K. When you divide these standard deviations by the sqrt(n) for the same n, you get bigger MoEs in the second case.
Reply
  • You may want to mention that the main two determinants of the MoE are the sample size, as the square root of the n (lower for a tract than for a county, in most situations), roughly (there are technicalities), and the mean income itself. I think of income as approximately constant coefficient of variation variable. Coefficient of variation = standard deviation in the population / mean. For a ZIP code with mean income of $15K, you can expect the standard deviation to be may be $20K, and for a ZIP code with mean income of $100K, the standard deviation could be $130K. When you divide these standard deviations by the sqrt(n) for the same n, you get bigger MoEs in the second case.
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