124 ables to account for spatial relationships among points. The first ten spatial filters were included as independent variables alongside community socioeconomic characteristics in the construc- tion of each region’s logistic regression model. The decision to use ten spatial filters was based on sequentially adding filters until the Moran’s I statistic for model residuals was <0.05 in the first distance class (following de Oliveira and Diniz- Filho 2010). Overall model fit was assessed using the McFadden pseudo-R2 values than traditional R2 ; this metric yields lower calculations, as values from 0.20–0.40 represent excellent model fit (McFadden 1979). SEVM and logistic regressions were performed in SAM v4.0 (Rangel et al. 2010). RESULTS TCUSA Participation Varies by Region In total, 2,673 candidate communities partici- pated in TCUSA. These communities repre- sented 132,271,497 people, or 53.9% of the total population in candidate communities. Among all candidate communities, the TCUSA participa- tion rate was 23.5%, and ranged from 11.5% in the Middle Atlantic region to 44.4% in the West North Central region (Table 1). The regional comparison of TCUSA participation rates in- dicated highly significant differences among regions (χ2 = 827.7, P < 0.001). TCUSA par- ticipation rates were relatively low in New Eng- land, Middle Atlantic, West South Central, and Pacific regions. Conversely, participation rates were relatively high in East North Central, West North Central, and Mountain regions (Table 1). Berland et al.: Assessment of Tree City Participation Table 1. Tree City USA (TCUSA) participation rates by U.S. region. Chi-square post hoc tests were used to determine whether each region’s participation rate was High, Low, or not significantly different (ns) from the rest of the U.S. (χ2 interpretation). Region 1-New England 2-Middle Atlantic 3-East North Central 4-West North Central 5-South Atlantic 6-East South Central 7-West South Central 8-Mountain 9-Pacific United States z For communities ≥2,500 population Community Population Relates to Likelihood and Duration of TCUSA Participation The logistic regression models predicting TCUSA participation as a function of popula- tion were highly significant (P < 0.0001) for the national data set (Table 2; Figure 2) and for each U.S. region (Figure 3). In each model, the like- lihood of TCUSA participation increased with population. Nationally, the predicted popula- tion at which a community had a 0.5 prob- ability of participating was 46,262, but this value varied widely among regions (Table 2). To assess the relationship between year of TCUSA adoption and community population, researchers used a linear regression with qua- dratic term based on its lower AIC score (8,573.4 versus 8,585.2 for the model without quadratic term). The model fit was highly significant (P = 0.0002), but the overall explanatory power of the model was limited (adjusted R2 = 0.05). The regres- Table 2. Logistic regression results predicting likelihood of Tree City USA participation as a function of community popula- tion (log). Region 1-New England 2-Middle Atlantic 3-East North Central 4-West North Central 5-South Atlantic 6-East South Central 7-West South Central 8-Mountain 9-Pacific United States n 736 2,617 1,617 810 1,906 602 1,062 647 1,358 11,355 Estimate 1.05 0.90 0.83 1.14 0.86 1.09 1.13 0.63 0.96 0.83 SE 0.11 0.07 0.06 0.10 0.06 0.12 0.09 0.08 0.07 0.02 z-ratio 9.3 13.6 13.6 11.5 15.0 8.9 12.0 8.0 14.1 35.6 z The predicted population at which a community has a 0.5 probability of participating in Tree City USA. P <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 Pop. at 0.5 probabilityz 54,553 96,034 15,979 9,922 48,823 28,405 80,731 22,177 79,342 46,262 % TCUSAz 19.2% 11.5% 39.7% 44.4% 23.1% 23.4% 12.1% 39.1% 19.7% 23.5% χ2 interp. Low Low High High ns ns Low High Low ©2016 International Society of Arboriculture
March 2016
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