Lab7_with_answers

Lab7_with_answers - BIOL 361 LAB 7 Categorical Data...

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BIOL 361 LAB 7 Categorical Data Analysis March 10, 2009 Question 1 : An investigator set up an experiment involving the effect of different light treatments on the gastropod Littorina . The light treatments consisted of three different light zones (with green light filtered out [zone 1], blue light filtered out [zone 2], red light filtered out [zone 3]), and a sample of 33 gastropods that were each released to choose one of the light zones. The result of the experiment was 15 gastropods in zone 1, 12 gastropods in zone 2 and 6 gastropods in zone 3. Test the hypothesis (alpha = 0.05) that the light treatments had no effect on the distribution of gastropods. Answer: H o : The light treatments have no effect on the distribution of gastropods (Or, in the statistical population, there is a 1:1:1 ratio of choice by the gastropods among green, blue and red light filtered out) (or, gastropods show no preference for any of the light treatments). H 1 : The light gradient has an effect on the distribution of gastropods (The ratio is not equal to 1:1:1) (Gastropods show a preference for at least one of the light treatments) Appropriate test is Chi-squared test (1-way GOF test using the Chi- square test statistic) In SPSS, enter the data (1, 2 and 3 for light categories), enter 15 1’s, 12 2’s and 6 3’s into one variable. Analyse Æ nonparametric tests Æ Chi-square Æ select variable Æ Expected = all values equal Littorina frequency 15 11.0 4.0 12 11.0 1.0 6 11.0 -5.0 33 1 2 3 Total Observed N Expected N Residual 1
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Test Statistics 3.818 2 .148 Chi-Square a df Asymp. Sig. Littorina
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Lab7_with_answers - BIOL 361 LAB 7 Categorical Data...

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