Oct 13 - Statistics

Oct 13 - Statistics - Thursday, October 13, 2011 Statistics...

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Thursday, October 13, 2011 Statistics Distributions Central Tendency Variability Distributions Simplify with a few numbers (Statistics) Mean (); M Add up numbers & divide by N (the number of students) (xmas) = 60.69 average grade for the Christmas exam Median (MDN) Midpoint of ranked distribution List of numbers, find median. Rank from low to high. MDN (xmas) = 54 Note: N = 1135 Look at the score in the middle, i.e., score #568 (This leaves 567 scores on each “side”) Mode Most frequent score Easy to identify from frequency distribution Mode xmas = 54 (Frequency = 47) Note: ≈ MDN ≈ MODE Shape (of frequency distribution curve) Overall shape determined by dispersion of scores… 1
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Thursday, October 13, 2011 How do they cluster around the mean? Range: Difference between highest and lowest scores. XMAS 98 – 24 = 74 Note: 1. Range influenced by extreme scores 2. Same value can be obtained with a variety of scores, e.g., 84 – 10 – 74 Variance (s 2 ) Degree of fluctuation of scores around the mean Some distributions have high variance, others are relatively low
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Oct 13 - Statistics - Thursday, October 13, 2011 Statistics...

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