Table 1. Results from our model-selection procedure used to select the number of NPI periods in each region.

Region	ΔAICc	ΔBIC
Navajo Nation	-6.4	-15.7
Arizona	76.2	66.7
Colorado	108.3	99.1
New Mexico	56.6	47.4
Utah	98.1	89.0

We calculated the value of the Akaike information criterion corrected for small sample size (AICc) for n = 0 and n = 1 versions of the model, as well as and value of the Bayesian information criterion (BIC) for the same two versions of each model. We defined ΔAICc = AICc^{n = 0} − AICc^{n = 1} and BIC = BIC^{n = 0} − BIC^{n = 1}. We adopted n = 1 over n = 0 when ΔAICc > 10 and ΔBIC > 10 (i.e., we reject the hypothesis that n = 0 when both ΔAICc and ΔBIC are greater than 10). Accordingly, n = 0 is indicated only for the Navajo Nation and n > 0 is indicated for all four surrounding states.