The purpose of this article is to highlight different ways of using data from large-scale-studies to interpret trends in the Swedish results in science during the last decade. A majority of the PISA- and TIMSS-studies during this period indicates a clear descending trend in the Swedish national mean values and in some studies the Swedish results display the most significant downward results of all countries. This article discusses how this development may be explained and to what extent the national mean values may be understood as trustworthy. In alternative studies some researchers have used the data to conduct secondary analyzes and show that the trend only are valid in some performance groups and that the reduced results in the group of low- and mid-performers explains the main part of the descending national trend. In addition, these studies indicate that increased school segregation and the development of decreased equity between schools may explain the trend in science during the last decade.