Chi square calculation

Chi square calculation - Tutorial on Using the 2 X test for...

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Null Hypothesis and Alternate Hypothesis H 0 - Null Hypothesis: The Numbers of Wolbachia Infections in Ant Population A and Population B are the same (homogenous). H 1 (or H a ) - Alternate Hypothesis: The Numbers of Wolbachia Infections in Ant Population A and Population B are different (heterogenous). Tutorial on Using the X 2 test for Homogeneity Testing for Uniformity or Difference in Wolbachia Infection Rates Between Two Populations of Ants Wednesday, November 9, 2011

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Category 1 WSP+ Infected Category 2 Uninfected Totals Population A 31 19 50 Population B 18 34 52 Totals 49 53 102 Setting Up Populations and Categories for the X 2 Test for Homogeneity Construct a data table like this one: Row A Row B a,1 a,2 b,1 b,2 a,1 + a,2 + b,1 + b,2 a,1 + b,1 a,2 + b,2 a,1 + a,2 b,1 + b,2 Column 1 Column 2 Entire Population Each Category of each Population has an Observed and an Expected Number. To find the Expected number you must find the five Marginal Totals. Add values in each row and column to find these Marginal Totals. From these you proceed to the next step to find the Expected number for each Category of each Population. Table 1: Observed Ant Infection Numbers for Wolbachia and Marginal Totals Wednesday, November 9, 2011
Finding the Expected number for each Category of each Population. E r,c = n r X n c / n E a,1 E a,2 E b,1 E b,2 E r,c = Expected for a particular category/population cell n r = row Marginal Total n c = column Marginal Total n = grand Total Four Expected numbers are calculated for each of the four Observed values. Each E-value is found by multiplying the a cell’s Marginal Totals for the row and column divided by the grand total of all the populations. Table 2: Expected Numbers of Wolbachia Infected and Uninfected Ants Category 1 WSP+ Category 2 Uninfected Totals Population A 31 19 50 Population B 18 34 52 Totals 49 53 102 Table 1: Observed Ant Infection Numbers for Wolbachia and Marginal Totals Wednesday, November 9, 2011

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E a,1 = 50 X 49 102 = 24.02 E a,2 E b,1 E b,2 Finding the Expected number for each Category of each Population. E
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This note was uploaded on 02/09/2012 for the course BIOLOGY 102 taught by Professor Anderson during the Spring '11 term at Harvard.

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Chi square calculation - Tutorial on Using the 2 X test for...

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