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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 Chisquared test (1way 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
Chisquare
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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View Full DocumentTest Statistics
3.818
2
.148
ChiSquare
a
df
Asymp. Sig.
Littorina
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