“…The most serious error frequently made is the misinterpretation of results caused by the faulty assumption that there is no test-retest effect and that consequently differences between the initial and final test scores should be attributed to some external variable (7, 10, 11, 89,95,97). This error is common in the interpretation of test scores of individual clinical cases (3,20,30,46,65,68,75,93,96).…”