In Germany, three large-scale surveys–the Level One Study (LEO), the Programme for the International Assessment of Adult Competencies (PIAAC), and the National Educational Panel Study (NEPS)–provide complementary data on adults’ literacy skills that can be harnessed to study adults with low literacy. To ensure that research on low-literate adults using these surveys arrives at valid and robust conclusions, it is imperative to ascertain the comparability of the three surveys’ low-literacy samples. Towards that end, in the present study, we comprehensively assess the comparability of adults with low literacy across these surveys with regard to their sociodemographic and socioeconomic characteristics.

We used data from LEO, PIAAC, and NEPS. We identified features of the sample representation and measurement of (low) literacy as potential causes for variations in the low-literacy samples across the surveys. We then compared the low-literacy samples with regard to their sociodemographic and socioeconomic characteristics and performed logistic regressions to compare the relative importance of these characteristics as correlates of low literacy.

The key insight our study provides is that–despite different sample representations and measurement approaches–the low-literacy samples in the three surveys are largely comparable in terms of their socioeconomic and sociodemographic characteristics. Although there were small differences between the surveys with regard to the distribution of gender, educational attainment, and the proportion of non-native speakers within the group of low-literate adults, results revealed that both the prevalence of low literacy and its correlates were largely robust across LEO, PIAAC, and NEPS. Across all three surveys, lower educational attainment emerged as the most significant correlate of low literacy, followed by a non-German language background, unemployment and low occupational status.

Our study provides evidence that all three surveys can be used for investigating adults with low literacy. The small differences between the low-literacy samples across the three surveys appear to be associated with sample representation and certain assessment features that should be kept in mind when using the surveys for research and policy purposes. Nevertheless, our study showed that we do not compare apples with oranges when dealing with low-literate adults across different large-scale surveys.