The term feeble-minded was used from the late nineteenth century in Great Britain, Europe and the United States for disorders later referred to as illnesses or deficiencies of the mind. At the time, mental deficiency encompassed all degrees of educational and social deficiency. Within the concept of mental deficiency, researchers established a hierarchy, ranging from idiocy, at the most severe end of the scale; to imbecility, at the median point; and to feeble-mindedness at the highest end of functioning. The latter was conceived of as a form of high-grade mental deficiency.