Table 4.

Medians and ranges for hormone levels by production method (conventional v. organic) in the set of retail milk samples collected in nine continental US regions, August 2015

Hormones	FDA limit	Conventional (n 35)		Organic (n 34)		P value*
		Median (ng/ml)	Range (ng/ml)	Median (ng/ml)	Range (ng/ml)
bGH	NA	9·8	0·6–17·0	0·5	<0·4–4·6	<0·0001
IGF-1	NA	3·5	0·3–8·1	1·1	<0·1–3·8	<0·0001

FDA, US Food and Drug Adminisitration; bGH, bovine growth hormone; IGF-1; insulin-like growth factor 1; NA, not applicable; LOD, limit of detection.

Estimated values for samples <LOD were imputed at ½ × LOD for purposes of testing the differences between groups.

^*P value for conventional v. organic: Wilcoxon rank-sum test (P < 0·05 considered statistically significant).