In cross-national studies, mean levels of self-reported phenomena are often not congruent with more objective criteria. One prominent explanation for such findings is that people make self-report judgements in relation to culture-specific standards (often called the reference group effect), thereby undermining the cross-cultural comparability of the judgements. We employed a simple method called anchoring vignettes in order to test whether people from 21 different countries have varying standards for Conscientiousness, a Big Five personality trait that has repeatedly shown unexpected nation-level relationships with external criteria. Participants rated their own Conscientiousness and that of 30 hypothetical persons portrayed in short vignettes. The latter type of ratings was expected to reveal individual differences in standards of Conscientiousness. The vignettes were rated relatively similarly in all countries, suggesting no substantial culture-related differences in standards for Conscientiousness. Controlling for the small differences in standards did not substantially change the rankings of countries on mean self-ratings or the predictive validities of these rankings for objective criteria. These findings are not consistent with mean self-rated Conscientiousness scores being influenced by culture-specific standards. The technique of anchoring vignettes can be used in various types of studies to assess the potentially confounding effects of reference levels.