In the comment section following my recent post on Energy access as a life-or-death issue, Paul comments on the plot showing a clear positive correlation between energy use and life expectancy, making the point that correlation does not imply causation. This led me to do a little more reading, and crystalize my thoughts on the issue. Here’s my detailed response:
First off, while it’s true that you can’t infer a causal mechanism from a simple correlation, neither my post nor the original linked to goes quite so far as to make that inference!! I use the terms ‘correlates’ and ‘associated’, while the original post says ‘factor which contributes’. So I think we both equivocated enough to be in the clear 🙂
Beyond the semantics, though, there are cases with regard to energy use where the slippery slope of correlation/causation is in fact less slippery than one might guess. This is particularly true for the transition from solid biomass combustion to more modern energy sources for household cooking. The science around the indoor air pollution derived from solid fuel combustion is robust enough to say definitively that transitioning from traditional biomass-fuelled indoor cooking to clean cooking technologies DOES IN FACT reduce morbidity- it has been demonstrated through randomized controlled trials. The authors of that study conclude:
“reducing household woodsmoke exposure is a public health intervention that is likely on a par with vaccinations and nutrition supplements for reducing severe pneumonia”
However, note that the ‘energy use’ World Bank development indicator plotted above does in fact include solid biomass use (I wouldn’t have thought so, but I just looked it up), so in this case upgrading to more modern cooking technologies doesn’t necessarily imply an increase in overall energy use (just as likely the opposite, since cooking with modern energy sources tends to be more energy efficient than cooking on solid biomass). So its unclear how cooking fuel switching shows up on the plot above.
It’s more challenging to draw robust conclusions about the presence of a causal relationship between broader energy access issues such as rural electrification and health outcomes- in that case doing a randomized control trial probably isn’t very practical! However, there is a large body of observational evidence suggesting that clean energy access is a necessary (but perhaps not sufficient) condition for economic development and associated health improvements, such as this recent study from authors at the World Bank:
I’ll end with a relevant quote from this World Bank paper:
“Quantifying the impact of energy services on human development is not easy. However, a lack of quantitative data does not suggest the absence of a relationship but rather the need for further analysis and research.”
FURTHER UPDATE: Dr. Pielke’s blog has a nice follow-up post showing the rate of rural electrification in different countries over time:
We just finished up a proposal for a rural electrification project in southeast Asia, and find it particularly interesting to see that Thailand showed by far the fastest rate of electrification of any country included! For reference, apparently most of their power generation comes from gas-fired plants (http://www.geni.org/globalenergy/library/energy-issues/thailand/index_chart.html).