jurans quality handbook - 1164
034003-x_Ch44_Juran
3/6/00 2:28 PM
Page 13
BASIC STATISTICAL METHODS
44.13
time of the third part to fail can sometimes serve to predict the average of all five, and thereby the decision of the test can be made much sooner. As shown on Figure 44.6, the median is simply the horizontal scale value where the percentile curve reaches the height 50 percent. The mode (the value that occurs most often in data) is used for severely skewed distributions, describing an irregular situation where two peaks are found, or for eliminating the effects of extreme values. The statistical “efficiency” of these measures varies. See Dixon and Massey (1969, chap. 9) or Dudewicz (1976, pp. 221–222) for elaboration. Measures of Dispersion. Data are always scattered around the zone of central tendency, and the extent of this scatter is called dispersion or variation. A measure of dispersion is the second of the two most fundamental measures in all statistical analysis.
TABLE 44.9 Percentile Rank of Resistance Values in Table 44.6
FIGURE 44.6
Percentile curve of a data set.
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