It might be useful to note that the Economist did not do this research. This is a summary of a study by an academic economist: https://papers.ssrn.com/sol3/pap

It might be useful to note that the Economist did not do this research. This is a summary of a study by an academic economist: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3882062 https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3882062 It's likely your questions are answered therein. EDIT: Skimming it briefly it seems like section 4, equation 4 is relevant to your criticism. It seems to be allowing for some level of independence in the internal relationship between a country's gdp growth and light, and trying to capture the parameter of interest in part fromm the within-country variation over time.