The data are dichotomous scores of a Dutch intelligence test on number completion (Dutch: "Cijferreeksen", Drenth and Hoolwerf, 1970). The file consists of archival data that were collected in a high-stakes personnel selection context around 1990.
A 1000x26 matrix of dichotomous item scores.
Drenth, P. J. D., and Hoolwerf, G. (1970) Numerieke aanleg test - Cijferreeksen (NAT-Cijferreeksen) [Numerical ability test]. Amsterdam: The Netherlands.