Abstract

Most philosophers of science now believe that scientific data are theory laden, i.e., the evaluation of data is influenced by prior theoretical beliefs. Although there is historical and psychological evidence that is consistent with the theory-laden position, experimental evidence is needed to directly test whether prior beliefs influence the evaluation of scientific data. In a fully counterbalanced design, one group of subjects received evidence that dinosaurs were cold-blooded, and another group of subjects received evidence that dinosaurs were warm-blooded. The subjects reported a strong belief in whichever theory they had read about. Then subjects were presented with a piece of data that supported one theory and contradicted the other theory. The identical piece of data was rated as more believable when it was consistent with the subject's theory than when it was inconsistent. These results provide clear support for the position that scientific data are theory laden.