I think the evidence presented is way too weak to support the type of conclusions drawn in this piece. I mean really, we’re computing doubling times by taking logarithms of estimated GDP, inserting an arbitrary offset in our definition of the horizontal axis and then plotting THAT on a log-log scale? What were you expecting to find?
More specifically: the horizontal labels of the most recent data points are heavily influenced by the particular choice of 2020 offset. I’ve taken the liberty of repeating (I hope) Scott’s analysis with the data from the paper, and swapping the offset to 2050 or even 2100 bunches the last data points a lot closer together, allowing a linear fit to pretty much pass through them. I think some argument can be made that we need a higher time resolution in an era with a doubling time of ~20 years compared to an era with a doubling time of ~500 years, but I’m still not happy with how sensitive this analysis is and would love to hear why 2020 is a better choice than 2100.
Also I notice that Scott left a bunch of data points from the paper out of the graph. I can live with excluding the really early ones (before 10000 B.C.), but why do you skip over the ones near 0 A.D.? The 1100-1200′s? And where are the data points with negative doubling times (i.e. declining GDP)? Maybe I missed it but I don’t see mention of these at all.
I think the evidence presented is way too weak to support the type of conclusions drawn in this piece. I mean really, we’re computing doubling times by taking logarithms of estimated GDP, inserting an arbitrary offset in our definition of the horizontal axis and then plotting THAT on a log-log scale? What were you expecting to find?
More specifically: the horizontal labels of the most recent data points are heavily influenced by the particular choice of 2020 offset. I’ve taken the liberty of repeating (I hope) Scott’s analysis with the data from the paper, and swapping the offset to 2050 or even 2100 bunches the last data points a lot closer together, allowing a linear fit to pretty much pass through them. I think some argument can be made that we need a higher time resolution in an era with a doubling time of ~20 years compared to an era with a doubling time of ~500 years, but I’m still not happy with how sensitive this analysis is and would love to hear why 2020 is a better choice than 2100.
Also I notice that Scott left a bunch of data points from the paper out of the graph. I can live with excluding the really early ones (before 10000 B.C.), but why do you skip over the ones near 0 A.D.? The 1100-1200′s? And where are the data points with negative doubling times (i.e. declining GDP)? Maybe I missed it but I don’t see mention of these at all.
I showed it that way because it made more sense to me. But if you want, see https://docs.google.com/spreadsheets/d/1xEkh4jhUup0qlG6EzBct6igvLPeRH4avpM5nZQ-dgek/edit#gid=478995971 for a graph by Paul where the horizontal axis is log(GDP); it is year-agnostic and shows the same pattern.
Thanks, that addresses the concerns I had!