Table 3.

PC₅₀ and logRTA values for STTA assay (parabens)

Test chemicals	STTA assay
	PC50 (M)	logRTA*
17β-estradiol	2.88 × 10−11	2
17α-estradiol	3.0 × 10−9	−0.01773
Butyl paraben	1.25 × 10−7	−1.63752
Ethyl paraben	1.26 × 10−6	−2.64016
Propyl paraben	2.0 × 10−6	−2.84164
Isobutyl paraben	6.3 × 10−7	−2.34008
Isopropyl paraben	1.58 × 10−6	−2.73993

^*Relative transcriptional activation is calculated as 100 × (PC₅₀) of E₂/(PC₅₀) of test compound, a value of 100 indicates that the compound tested is a full agonist.

Abbreviations: RTA, Relative transcriptional activation; PC₅₀, the concentration of chemical estimated to cause 50% of activity of the positive control response on a plate by plate basis.