Table 2.

Basic DID models of IRI for study design causality.

	$\beta$	SE	T statistics	R
Constant	998.24	0.82	795.011*	0.13
Block	10.29	1.252	10.273**	0.46
Alternating	25.63	1.449	13.255**	0.53
Block $\times$ alternating	15.41	1.502	3.685**	0.33
Obs			7023
BIC			393.5
Likelihood-ratio test of alpha = 0			Chibar2(01) = 143.3 Prob $\ge$ chibar2 = 0.001

SE Standard error, $\beta$, Regression coefficient, Prob Probability, obs Observation, BIC Bayesian information criterion.

*$P<0.01$, **$P<0.001$.