【正文】 only 13 Quartiles ? When an ordered set of data is divided into four equal parts,the division points are called quartiles. ? The first or lower quartile Q1 is a value that has approximately 25% of the observations below in value. ? The second quartile Q2 is a value that has approximately 50% of the observations below in value. It is also called the median. ? The third or upper quartile Q3 is a value that has approximately 75% of the observations below in value. Belton Confidential: For training only 14 Quartiles ? Twenty ordered observations on the times to failure (in hours) of electrical insulation material are shown below. 204 228 252 300 324 444 624 720 816 912 1176 1296 1392 1488 1512 2520 2856 3192 3528 3710 ? ?? ?? ?20xx22520xx121044211769123842444324321??????????x~QBelton Confidential: For training only 15 Measure of Dispersion ? Range (Will not be discussed) ? Variance (Will not be discussed) ? Standard Deviation (Will not be discussed) ? InterQuartile Range Belton Confidential: For training only 16 Interquartile range ? The interquartile range is another measure of dispersion. IQR = Q3 Q1 ? The interquartile range is less sensitive to extreme values in a sample than the range. ? For the two samples (1, 3, 5, 8, 9 and 1, 5, 5, 5, 9), their interquartile ranges are 5 and 0 respectively. Belton Confidential: For training only 17 Measure of Shape Skewness ? Skewness ? The degree of assymmetry of a distribution around its mean is referred to as its skewness. Belton Confidential: For training only 18 Measure of Shape Kurtosis ? Kurtosis ? Kurtosis characterizes the relative peakedness or flatness of a distribution pared to a normal (mesokurtic) distribution. Belton Confidential: For training only 19 MiniTab’s Descriptive Statistics ? Stat ? Basic Statistics ? Display Descriptive Statistics ? produces statistics for each column of data (or subsets within a column) and displays them in the Session Window and optionally in a graph ? the user has no control over which statistics are puted/displayed ? Stat ? Basic Statistics ? Store Descriptive Statistics ? descriptive statistics for each column (or subsets within a column) a