Question

There are two types of sneetches, the star-bellied sneetch (S. astra) and the plain sneetch (S. simplex). Professor O. B. Servant counted sightings of these sneetches, identified each sneetch he saw, and classified their location into the three types: Ground, Tree, and Lake. The number of sightings are shown in the table below:

	S. astra	S. simplex
Ground	90	88
Tree	83	57
Lake	82	80

Professor O. B. Servant would like to know if there is a difference in habitat use between the two types of sneetches.

Use the R function pchisq.test() to find the test statistic X2 for the test for independence, the degrees of freedom, and the p-value.

X2=

df=

p-value =

Answer 1

applying chi square test:

Expected	Ei=row total*column total/grand total	Astra	Simplex	Total
	Ground	94.56	83.44	178
	Tree	74.38	65.63	140
	Lake	86.06	75.94	162
	total	255	225	480
chi square    χ2	=(Oi-Ei)2/Ei	Astra	Simplex	Total
	Ground	0.2201	0.2495	0.470
	Tree	1.0002	1.1336	2.134
	Lake	0.1918	0.2173	0.409
	total	1.412	1.600	3.013

X2= 3.0125~ 3.013

degree of freedom(df) =(rows-1)*(columns-1)=

2

p value =0.2217