Question

A study was conducted to find out whether malaria infection rates in the Amazon differed by region. You use the chisq.test function with these data.

	Region
Infection	east	central	west
Yes	5	10	7
No	50	30	47

Pearson's Chi-squared test

data: infect

X-squared = 4.8759, df = 2, p-value = 0.08734

What are the degrees of freedom for the test? (3pts)

	A.	2
	B.	5
	C.	4
	D.	6

A study was conducted to find out whether malaria infection rates in the Amazon differed by region. You use the chisq.test function with these data.

	Region
Infection	east	central	west
Yes	5	10	7
No	50	30	47

Pearson's Chi-squared test

data: infect

X-squared = 4.8759, df = 2, p-value = 0.08734

What are the null and alternative hypotheses for this test? (3 pts)

Answer 1

(a): In the contingency table, the number of rows (r) is 2 and the number of columns (c) is 3.

The degrees of freedom (df) for the test can be calculated as:

Therefore, the required degrees of freedom is 2.

Hence, the correct option is A.

(b): The researcher wants to check whether malaria infection rates in the Amazon differed by region.

The null (Ho) and the alternative hypothesis (Ha) is:

Ho: The malaria infection rates are independent of regions (east, central and west).

Ha: The malaria infection rates are not independent of regions (east, central and west).

Or

In other words, the null (Ho) and the alternative hypothesis (Ha) can be framed as:

Ho: There is no relationship between malaria infection rates and regions (east, central and west).

Ha: There is a relationship between malaria infection rates and regions (east, central and west).