Table 1

Comparison of Treated and Control Counties in 1930

	More Treated			Less (or Not) Treated
	Proportion within the 100-Mile-Wide Shelterbelt Zone >50%			Proportion within the 100-Mile-Wide Shelterbelt Zone <50%
Variables^{^a}	Obs.	Mean	S.D.	Obs.	Mean	S.D.	Difference
Proportion protected by shelterbelts	117	0.30	0.28	117	0.19	0.28	0.11^*
Other Right-Hand-Side Variables
Proportion medium-eroded^{^b}	117	0.41	0.35	117	0.38	0.35	0.03
Proportion high-eroded^{^b}	117	0.20	0.32	117	0.13	0.26	0.07
Proportion above the Ogallala Aquifer^{^b}	117	0.32	0.42	117	0.37	0.45	-0.05
Total precipitation in recent 2 years (mm)	117	1,114.28	166.05	117	1,118.22	239.92	−3.94
Average temperature in recent 2 years (°C)	117	10.51	4.35	117	9.82	3.99	0.69
Farmland/county area	117	0.91	0.07	117	0.89	0.09	0.02
Woodland/county area	117	0.01	0.02	117	0.02	0.04	−0.01
Cropland/farmland	117	0.58	0.17	117	0.57	0.18	0.00
Population per 1,000 acres	117	21.22	11.38	117	26.15	29.24	−4.93
Fraction of rural population	117	0.90	0.16	117	0.86	0.22	0.04
Fraction of farming population	117	0.62	0.11	117	0.58	0.16	0.04^*
Number of farms/1,000 acres	117	2.64	1.23	117	2.63	1.50	0.01
Average farm size (in acres)	117	443.19	323.11	117	508.53	460.90	−65.33
Area of corn/cropland	117	0.17	0.19	117	0.17	0.17	0.00
Area of wheat/cropland	117	0.29	0.27	117	0.31	0.24	−0.02
Area of hay/cropland	117	0.11	0.13	117	0.13	0.14	−0.02
Area of cotton/cropland	117	0.12	0.25	117	0.05	0.15	0.07^*
Area of oat, barley, and rye/cropland	117	0.12	0.12	117	0.15	0.12	−0.03^*
Number of cows/1,000 acres	117	52.24	17.45	117	53.83	23.79	−1.60
Number of pigs/1,000 acres	117	52.38	63.31	117	57.40	76.20	−5.03
Number of chickens/1,000 acres	117	241.55	159.19	117	245.50	189.27	−3.95

↵a Main data source from the U.S. Department of Agriculture Census of Agriculture and Population; see Appendix B for more detailed definition of variables
↵b Soil erosion data from Hornbeck (2012); data on the Ogallala Aquifer from Hornbeck and Keskin (2014)
↵* t-test with p-value < 0.05