Introduction to Genetic Analysis 670

Introduction to Genetic Analysis 670 - 44200_20_p643-678...

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Statistical appendix 669 Number of Teeth in the Sex Comb on the Right ( x ) and Left ( y ) Legs and the Sum of the Two ( T ) for 20 Drosophila Males xy T n i f i 5 n i / N 65 1 1 1 5 0.05 66 1 2 57 1 2 3 5 0.15 1 2 76 1 3 58 1 3 4 5 0.20 67 1 3 1 3 86 1 4 68 1 4 77 1 4 1 4 7 5 0.35 1 4 1 4 1 4 87 1 5 78 1 5 3 5 0.15 69 1 5 88 1 6 79 1 6 N 5 20 5 6.25 5 7.05 5 13.70 cov xy 52 0.1325 r xy 0.1360 T s T 5 1.308 s 2 T 5 1.71 y s y 5 1.0722 s 2 y 5 1.1475 x s x 5 0.9096 s 2 x 5 0.8275 3 20 7 20 4 20 3 20 1 20 TABLE 20-3 Measures of dispersion: the variance A second characteristic of a distribution is the width of its spread around the central class. Two distributions with the same mean might differ very much in how closely the measurements are concentrated around the mean. The most common measure of variation around the center is the variance, which is deFned as the aver- age squared deviation of the observations from the mean, or When more than one individual has the same measured value, the variance can be written as To avoid subtracting every value of x separately from 5 o f i ( x i 2 x ) 2 s 2 5 f 1 ( x 1 2 x ) 2 1 f 2 ( x 2 2 x ) 2 1? ? ?1 f k ( x k 2 x ) 2 5 1 N o ( x i 2 x ) 2 5 ( x 1 2 x ) 2 ( x 2 2 x ) 2 ? ( x N 2 x ) 2 N variance 5 s 2
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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