Prof Zhang, Economist, Peking University says, regarding the results in his paper about the effects of pollution:
We are also puzzled by the difference in math and verbal tests as well as the gender difference.
Prof. Chew of National University of Singapore found similar results for college students, greater impact on male than on female students. He gave a talk last year at Peking University. However, in the later public version, his paper mainly emphasizes the impact on decision making. Perhaps he is leaving the findings on the impact on intelligence to another paper.
Because reviewers asked us to do so many robustness checks (in the end the appendix is 59 pages long), we didn’t have space to explore the heterogenous effect between rural and urban areas and across occupations in our paper.
In our paper, we didn’t compare the rural and urban sample. It is possible to run separate regressions to see if there are any systematic differences. Urban pollution has received more media attention although the surrounding areas may be more polluted. For example, most the pollutants for Beijing come from nearby counties in Hebei Provinces, where most polluted industries are located. In fact, air quality in many counties in Hebei province are worse than in Beijing.
In another related paper, we look at the impact of air pollution on happiness between those working indoors or outdoors and find indeed greater impact for those working outdoors. See the attached paper.
I suggested to Prof Zhang suppose that he might look back at those who were in very polluting occupations, and thus find the upper limits of the 3 year effect.
In summary, these are interesting findings which will have to be followed up. At the moment the reported effect of pollution is perplexing, and we may need a better model of how pollutants affect the nervous system.