Carozza et al. midpoint of our incidence data. Of the 29 eli- gible state registries originally available for this study, no county identiﬁers were available for three and no NASS data were available for one. Eight of the state cancer registries did not have data available for all years of the study period, so counties from those registries were included only for years for which data were available. In addition, for some states, agricultural census data or age-speciﬁc population data were not available for every county, so those counties also were excluded from the analysis (n = 149), leaving a total of 25 U.S. states and 1,078 counties for inclusion in the ﬁnal analysis. Statistical analysis. We derived the percent cropland for each county by dividing total land used for crop production by total land in acres for that county. On the basis of natural breaks in the overall distribution of percent cropland in the study area, we assigned counties with a total percent cropland of < 20% percent to the referent category (n = 515). For the remaining counties, categories of medium (20% to < 60%; n = 318) and high (≥ 60%; n = 245) agricultural activity were created. For evalua- tion of risk associated with the six leading U.S. crops, counties were classiﬁed as “exposed” if that crop was grown in that county, regardless of the percent of the total cropland for the county, and exposed counties were compared with counties that had both no recorded acreage planted in that crop and cropland totaling < 20% of the total county area. For total cancers and then speciﬁc ICCC cancer subgroups, we compared the incidence rates in counties with low potential pesticide exposure to those with medium to high expo- sure, based on the categories for our surrogate of percent cropland. We estimated odds ratios (ORs) and associated 95% confidence inter- vals (CIs) by logistic regression, with adjust- ment for age and sex at the county level based on Census data provided by the SEER*Stat software. We also evaluated the data using Poisson regression, but results were equivalent to the logistic regression, so only those risk estimates are presented. All models were run in the SAS System for Windows V8 (SAS Institute Inc., Cary, NC). Results A total of 25 U.S. population-based cancer registries were included in the final study population (Figure 1), with a total average population at risk of 25,110,289 children 0–14 years of age (Table 1). The ﬁnal sample included > 1,000 counties. The mean county size in acres was 670,572, and county size ranged from 15,796 acres in Rhode Island to Figure 1. Location and category of agricultural activity for counties included in the study. Table 1. Characteristics of the population-based U.S. cancer registries included in the study, NAACCR, 1995–2001. Population at risk (no.)a Childhood cancer incidence rateb County size (acres) Mean Minimum Percent county cropland No.c Mean ± SD Agricultural activity Missing or no data Low Medium High State (data years) Alabama (1998–2001) Arizona (1995–2001) Delaware (1997–2000) Florida (1995–2001) Idaho (1995–2001) Illinois (1995–2001) Indiana (1998–2001) Iowa (1995–2001) Kentucky (1995–2001) Louisiana (1995–2001) Maine (1995–2001) Massachusetts (1997–2001) Nebraska (1995–2001) New Hampshire (1999–2001) New Jersey (1995–2001) New Mexico (1995–2001) New York (1997–2001) Oregon (1996–2001) Rhode Island (1995–2001) South Carolina (1997–2001) Utah (1995–2001) Washington (1995–2001) West Virginia (1995–2001) Wisconsin (1995–2001) Wyoming (1995–2001) Total 560 923,182 1,093,842 158,387 2,990,616 295,656 2,686,668 1,306,617 592,570 809,827 1,009,052 246,630 1,244,435 367,540 255,944 1,728,136 419,775 3,891,864 692,795 203,255 827,867 577,001 1,232,017 333,797 1,117,019 105,796 25,110,289 108.6 128.8 155.1 148.9 147.8 144.8 142.7 158.2 147.1 116.6 173.8 152.8 128.7 120.4 155.9 127.1 154.4 146.8 180.4 129.3 142.2 157.8 133.7 148.6 156.0 145.5 aAverage annual population at risk, children 0–14 years of age. bRates are average annual per 100,000,000 population for 0–14 years of age and are age-adjusted to the 2000 U.S. stan- dard million population. cDifferences in county numbers are attributed to missing agricultural census data or age-speciﬁc population data. VOLUME 116 | NUMBER 4 | April 2008 • Environmental Health Perspectives SE 5.4 4.1 15.7 2.7 8.5 2.8 5.2 6.2 5.1 4.1 10.2 5.0 7.1 12.7 3.6 6.6 2.8 6.0 11.3 5.6 5.9 4.3 7.6 4.4 14.7 1.0 No. 67 15 3 67 44 102 92 99 120 64 16 14 93 10 21 33 62 36 5 46 29 39 55 72 23 1,227 484,778 4,848,735 416,985 515,795 1,203,650 348,821 249,531 361,211 211,906 435,661 1,234,581 358,306 529,051 574,040 235,910 2,353,736 495,022 1,706,711 133,759 418,937 1,813,366 1,092,615 280,280 482,788 2,702,040 670,572 342,296 792,158 272,831 153,791 260,816 102,274 55,508 243,884 63,258 115,616 162,566 30,580 154,030 236,051 66,104 69,987 18,162 278,570 15,796 230,140 194,875 111,963 53,149 148,456 1,282,556 15,796 Maximum 1,021,780 11,916,244 600,101 1,301,974 5,430,522 757,530 420,662 622,766 504,145 850,245 4,270,039 968,424 3,814,878 1,152,415 515,052 4,434,092 1,718,863 6,486,330 264,506 725,577 5,005,263 3,371,698 665,470 988,848 6,672,552 11,916,244 57 10 3 60 37 95 83 91 109 60 16 12 58 10 20 23 57 34 5 43 25 34 50 68 18 1,078 13.0 ± 8.0 1.8 ± 2.3 37.0 ± 11.0 10.3 ± 9.1 20.0 ± 16.7 66.6 ± 17.5 56.6 ± 18.7 74.7 ± 11.0 34.6 ± 20.9 19.9 ± 19.0 3.6 ± 2.3 4.2 ± 2.1 63.6 ± 19.1 2.6 ± 1.0 11.6 ± 10.3 5.3 ± 10.8 17.8 ± 13.0 10.5 ± 10.7 5.5 ± 4.0 13.6 ± 8.3 5.6 ± 5.4 17.0 ± 23.2 9.9 ± 7.2 34.4 ± 18.5 5.7 ± 4.8 32.3 ± 28.3