BIOL 373 Lecture Notes - Lecture 20: Biostatistics, Count Data, Test Statistic

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28 Dec 2015
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: actual frequency or count in the ith category. : expected frequency in the ith category if h0 true. Note: actual frequencies must be used, not proportions: reject h0 if calculated x2 critical x2. Where = k 1 and k is the number of categories. Example: hypothesis, wing-spot colour in mormon fritillary butterflies is controlled by a gene with 2 alleles, hypothesis: Wing-spot colour in mormon fritillary butterflies is controlled by a gene with 2 alleles, yellow spots completely dominant over silver spots. H0: wing-spot colour in butterflies is consistent with a 1:3 ratio. Ha: wing-spot colour not consistent with a 1:3 ratio: predicted: Conclude that the ratio of silver:yellow is not significantly different. Problems associated with the chi-square test: chi-square calculations are discrete, but the theoretical x2 distribution is, bias: calculated values will be larger than the theoretical values they are from 1:3 continuous estimating. The continuous approximation works well except when k = 2.

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