Knox's "Cube Imitation" Test

"A scale, based on the work at Ellis Island, for estimating mental defect" by Howard A. Knox, M.D., Assistant Surgeon, US Public Health Service, is the lead article in The Journal of the American Medical Association, March 7, 1914, LXII, 10, 741-747.

Dr. Knox writes: "From different sources have come many requests for the description of the tests worked out and conclusions reached in the practical work that has been done on Ellis Island on mental defectives. For this reason I present this paper, based on tests which I have made on over 4,000 suspected defectives in the last eighteen months and many more made by my associates ... all were considered sufficiently near the required standard to be allowed to pass, except 400 certified as feeble-minded and (in a few cases) as imbeciles."

Among the series of tests administered was "Knox's cube imitation test", now known as the "Knox Cube Test." Here is his description, which is the caption of Knox's Figure below. "Four 1-inch [black] cubes, 4 inches apart, are fastened to a piece of thin boarding. The movements and tapping are done with a smaller cube. The operator moves the cube from left to right facing the subject, and after completing each movement, the latter is asked to do likewise. Line a is tried first, then b, and so on to e. Three trials are given if necessary on lines a, b, c, and d, and five trials if needed on line e. To obtain the correct perspective the subject should be two feet from the cubes. The movements of the operator should be slow and deliberate." (The original apparatus is on display on Ellis Island.)

According to Dr. Knox, line a (1-2-3-4) should be accomplished at 4 years, b (1-2-3-4-3) at 5 years, c (1-2-3-4-2) at 6 years, d (1-3-2-4) at 8 years, e (1-3-4-2-3-1) at 11 years. Line d survived to form part of the 18-item Arthur (1947) version of the Knox Cube Test described in "Best Test Design" (Wright & Stone, 1979). Lines a, b, and c were reintroduced by Wright and Stone into their KCTB instrument.

John Michael Linacre

Knox's "Cube Imitation" Test Knox, H.A. … Rasch Measurement Transactions, 1999, 13:3 p. 708

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