This study aims to investigate how test scores from PIAAC (Programme for the International Assessment of Adult Competencies) can be interpreted, by comparing the PIAAC competencies literacy and numeracy to reasoning and perceptual speed. Dimensionality analyses supported, that the PIAAC competencies can be separated into a common factor overlapping with reasoning and perceptual speed, and domain-specific factors. For the common and specific factors, relations to other variables were analyzed. The nested factor for PIAAC literacy was as expected unrelated to age, positively related to learning opportunities during one’s lifetime, and positively related to literacy skill use. The nested factor for PIAAC numeracy was also as expected unrelated to age, against expectation unrelated to learning opportunities during one’s lifetime, and as expected positively related to numeracy skill use. Results support the validity of the intended test score interpretation for PIAAC literacy, while results for PIAAC numeracy were less clear.