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Unformatted text preview: such as height, yet, because of an environmental differ- ence between generations, every child might be taller than its parents. This phenomenon appears in adoption studies, in which children may be correlated with their biological parents but, on the average, may be quite dif- ferent from the parents as a result of a change in their social situation. Covariance and the variance of a sum In Table 20-3, the variances of the left and right legs are 0.8275 and 1.1475, which adds up to 1.975, but the variance of the sum of the two legs T is only 1.71. That is, the variance of the whole is less than the sum of the variances of the parts. This discrepancy is a consequence of the negative correlation between left and right sides. Larger left sides are associated with smaller right sides and vice versa, and so the sum of the two sides varies less than each side separately. If, on the other hand, there were a positive correlation between sides, then larger left and right sides would go together and the variation of the sum of the two sides would be larger than the sum of the two sepa-...
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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.
- Spring '08