Table 1.

Comparison of the characteristics of counties included and not included in the multilevel analysis

	Counties included in analysis (n=658)	Counties not included in analysis (n=2561)		All counties in the U.S. (n=3219)
	Median (minimum–maximum)	Median (minimum–maximum)	p value	Median (minimum–maximum)
Percent of families below federal poverty line	8.2% (1.6–45.1)	10.1% (0.0–64.1)	0.163	9.7% (0.0–64.1)
Population density (residents per square mile)	146.8 (1.7–45,519.3)	35.1 (0.0–5646.7)	<0.001	42.0 (0.0–45,519.3)
In metropolitan area	61.3%	19.4%	<0.001	28.0%
Percent African American	3.1% (0.0–67.1)	1.5% (0.0–86.1)	0.010	1.8% (0.0–86.1)