Judith Schrenk and Christine Gürtler, psychologists at the Max Planck Institute for Human Development, in Berlin, surveyed 234 children in the third and fifth grades from ten different elementary schools.
Judith Schrenk dan Christine Gürtler, psikolog di Institut Pengembangan Manusia Max Planck, di Berlin, menyurvei 234 anak kelas tiga dan lima dari sepuluh sekolah dasar.