The object of this study is to explore to what degree the question of ingroup favouritism, brought to light in the framework of ‘social identity theory’, is dependent upon the methods used for measuring this variable. The influence of this factor on ingroup bias was tested under the following three conditions: ‘complementary assessment’, ‘separate assessment’ and ‘choice of dimensions’. This last condition gave the subjects the opportunity to choose which dimensions would be used for assessment. It was found that the degree of ingroup bias is different for each of the three conditions. The results indicate that it is only under certain circumstances that the ingroup distinguishes itself as ‘better’ at the expense of the outgroup. This occurs only if the subjects are not given the opportunity to assess both groups on non-corresponding dimensions, and therefore do not have the possibility to rate them ‘equally good’ but ‘different’.