Monday, August 25, 2008

Simpson's Paradox in Bhutan

This year I am on academic sabbatical, hence the lower rate of postings. Moreover, postings this year might have an interesting twist, since I am in Bhutan volunteering at an IT Institute. As part of the effort, I am conducting workshops on various topics on the interface of IT and data analysis. IT is quite at its infancy here in Bhutan, which makes me assess and use IT very differently than I am used to.

My first posting is about Simpson's paradox arising in a Bhutanese context (I will post separately on Simpson's Paradox in the future): The Bhutan Survey of Standards of Living, conducted by the Bhutan National Statistics Bureau, reports statistics on family size, gender of the head-of-family, and rural/urban location. Let's consider the question whether family planning policies should be aimed separately at female- vs. male-headed families, or not. I was able to assemble the following pivot table from their online report:

Now, note the column marginal, where it appears that the average household size is identical for female-headed (4.9985) and male-headed (5.027) households. If you only sliced the data by the gender of the head of family, you might reach the conclusion that the same family planning policy should be used in both cases. Now, examine the figures broken down by urban/rural: Female-headed households are on average smaller than male-headed households in both urban and rural areas! Thus, family planning policies seem to need stronger (or at least different) targeting at male-headed households!

If you are not familiar with Simpson's Paradox you might be puzzled. I will write about the inner workings of this so-called paradox in the near future. Until then, check out Wikipedia...