Reviewing the history of international large-scale assessments (ILSAs), Gustafsson (2008) identified two phases in the work of the International Association for the Evaluation of Educational Achievement (IEA) demarcated by the setup of the new organization in 1990. During the first phase, the IEA conducted separate ILSAs in mathematics and science on four occasions; data were collected on mathematics in 1964 and 1980–82 and on science in 1970–71 and 1983–84. In the second phase, the Third International Mathematics and Science Study in 1995 was the first IEA study to test mathematics and science together. The assessment has been repeated every fourth year, most recently in 2019. Since 1999, the survey is named Trends in International Mathematics and Science Study (TIMSS).

The IEA studies from the first phase have not officially been linked to the TIMSS reporting scale. Previous research has shown that it is possible to link the cognitive outcomes from the two phases of IEA ILSAs on reading and mathematics (Afrassa, 2005; Majoros et al., 2021; Strietholt & Rosén, 2016). However, the studies on mathematics (Afrassa, 2005; Majoros et al., 2021) remained limited in terms of the comparability with the TIMSS reporting scale and the scope of educational systems included in the linking.

Afrassa (2005) used Australian data from the first three IEA ILSAs on mathematics and applied Rasch model equating procedures. Majoros et al. (2021) used data from four countries, England, Israel, Japan, and the USA, and all time points between 1964 and 2015, and applied concurrent calibration using the two-parameter logistic (2PL) model and the generalized partial credit model (GPCM; Muraki, 1992).

The present study aims to link the mathematics and science assessments from the first phase of IEA to the TIMSS reporting scales. This study builds on Majoros et al. (2021) and extends the scope of the linking. Firstly, it uses grade eight data from all participating educational systems. This means 83 educational systems in the studies on mathematics and 85 on science. Secondly, an alternative linking approach is employed to place the results of the first-phase studies on mathematics and science onto the TIMSS trend scale.

The scales achieved by this study may facilitate country-level longitudinal analyses. It is a well-known concern among researchers in the field of social sciences, that due to the cross-sectional survey designs of ILSAs, it is difficult to draw causal inferences about the data (see e.g., Allardt, 1990; Rutkowski & Delandshere, 2016). However, as Gustafsson (2008) pointed out, there are valid approaches to causal interpretation of ILSA data, that have been recently developed, for instance, in the field of econometrics. Suggestions for statistical methods for drawing causal inferences from ILSA data have been made by several researchers (Gustafsson, 2008; Gustafsson & Nilsen, 2022; Robinson, 2013). These powerful analytical approaches such as country-level longitudinal modeling techniques and advanced econometric methods allow for investigating changes in educational systems on the national level or in an international comparative context.