Table 11.

Robustness to Alternative Theories and Time-Invariant Country Fixed Effects

	(1)	(2)	(3)
	OLS	OLS	OLS
	Full Sample	Income Sample	Income Sample
	Dependent Variable is Diff. in:
	Log Population Density between 1 CE and 1000 CE		Log Income per Capita between 1 CE and 1000 CE
Diff. in Log Technology Index between 1000 BCE and 1 CE	1.747*** (0.429)	3.133* (1.550)	0.073 (0.265)
Constant	0.451*** (0.053)	−0.026 (0.204)	−0.040 (0.064)
Observations	126	26	26
R-squared	0.17	0.34	0.00

Summary – This table establishes that the change in the level of technological sophistication that occurred between the years 1000 BCE and 1 CE was primarily associated with a change in population density as opposed to a change in income per capita over the 1–1000 CE time horizon, and also reveals that there was no trend growth in income per capita during this period, thereby demonstrating robustness to time-invariant country fixed effects and dispelling an alternative migration-driven theory that is consistent with the level regression results.

Notes – (i) the technology index for a given time period reflects the average degree of technological sophistication across communications, transportation, industrial, and agricultural sectors in that period; (ii) the absence of controls from both regressions is justified by the removal of time-invariant country fixed effects through the application of the first-difference methodology; (iii) robust standard error estimates are reported in parentheses; (iv) *** denotes statistical significance at the 1 percent level, ** at the 5 percent level, and * at the 10 percent level, all for two-sided hypothesis tests.