What I think would be very interesting, though highly difficult I suspect, would be a control variable related to social institutional factors. While improvements in both economic productivity and technology should support increased population growth, so would more stable and peaceful societies.
In that regard I think I would start looking at for the decline in the first millennia AD would be related to social environment and institutions rather than economic—accepting that there will be some close links between social and economic outcomes that might be hard to separate.
What I think would be very interesting, though highly difficult I suspect, would be a control variable related to social institutional factors. While improvements in both economic productivity and technology should support increased population growth, so would more stable and peaceful societies.
In that regard I think I would start looking at for the decline in the first millennia AD would be related to social environment and institutions rather than economic—accepting that there will be some close links between social and economic outcomes that might be hard to separate.