“…Because a single extreme outlier can produce a detrimental effect on the PND score (Scruggs et al, 1987). Researches with results that have a data point reaching ceiling or floor in the baseline phase were found in Billings and Wasik (1985); Blick and Test (1987); Brigham, Hopper, Hill, Armas, and Newsom (1985); Burgio, Whitman, and Johnson (1980); Burgio, Whitman, and Reid (1983); Carr and Punzo (1993); Dunlap and Dunlap (1989); Glomb and West (1990); Gumpel and David (2000); Kern, Ringdah, Hilt, and Sterling-Turner (2001); Kern-Dunlap et al (1992); Kissel, Whitman, and Reid (1983); Koegel, Keogel, Hurley, and Frea (1992); Koegel and Frea (1993); Martin and Manno (1995); McKenzie and Rushall (1974); Olympia et al (1994); Stahmer and Schreibman (1992); Swanson (1981); Wilson, Leaf, and Nathan (1975); and Wood, Murdock, and Cronin, (2002).…”