Exploring the potential confounder of nitrogen fertilizers in the relationship between pesticide exposures and risk of leukemia: a Poisson regression with two-way fixed-effects analysis

Table 1 Association between 1-year lagged nitrogen use and cancer outcomes

Outcome	CCS^a	Model 1^b		Model 2^c		Model 3^d
Outcome	CCS^a	IRR (n = 249)	95% CI	IRR (n = 90)	95% CI	IRR (n = 249)	95% CI
Leukemia	39	0.95	0.93–0.98^*	0.93	0.88–0.98^*	0.95	0.93–0.98^*
NHL	38	0.98	0.94–1.02	0.92	0.87–0.98^*	0.97	0.94–1.01
MM	40	0.99	0.94–1.03	0.92	0.86–0.99^*	0.98	0.94–1.03

IRR incidence rate ratio, CI confidence interval
^* P < 0.05; residual deviance exceeds degrees of freedom so robust standard errors were applied using R (packages ggplot2 and sandwich). The fixed-effects approach demands a great number of parameter estimates which did not properly converge in our negative binomial regression, creating the incidental parameter bias and invalidating this option to correct for model overdispersion. The conditional and unconditional Poisson fixed-effects analyses produce identical estimates, however
^aUsing all International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes included in the Clinical Classification Software (CCS) in HCUP (1997–2007), as described in our prior investigation [3]
^bUnadjusted model, farm use of nitrogen fertilizers, as described in our prior investigation [3]
^cControlling for a 1-year lagged, logged measures of non-farm use of nitrogen fertilizers and pesticides, including atrazine, cypermethrin, dicamba, glyphosate, 2,4-D, and 2-methyl-4-chlorophenoxyacetic acid (MCPA), that are associated with arable agriculture crop production (United States Geological Survey, USGS) high estimates, years: 1996–2006) [3]
^dRemoving cypermethrin and MCPA data due to missingness

ISSN: 2523-3548