Responses to positively and negatively worded items are not always consistent, a behavioral pattern known as the item valence method effect. The current research employed latent difference (LD) modeling (Pohl, Steyer, & Kraus, 2008) to help determine explanations of the method effect. Respondents were more likely to reject negative characteristics (measured by negatively worded items) than to accept positive ones (measured by positively worded items), and supplementary analysis showed that this tendency was associated with social desirability response style. Correlations between the method effect and social desirability varied across Big Five personality traits, implying that social desirability cannot be the sole reason behind the phenomenon. Other possible explanations are discussed.