Field Ch. 19 - Chi Square

Question 1

Why use X^2 (chi square) test?

Answer 1

• analyzing categorical data

- compare observed frequencies to frequencies by chance

Question 2

How to calculate X^2?

Answer 2

start with a table of values: “observed”

1. (row total x column total)/grand total
   step 1 creates new table: “expected”
2. (observed - expected)^2/expected
   step 2 creates new table: “results”
3. X^2 = sum of results

Question 3

How to find P-value of X^2?

Answer 3

1. Go to Chi Square distribution table
2. Degrees of freedom: (rows - 1)(cols - 1)
3. Where does calculated X^2 land on table in DofF row?

this determines P-value (ex: p < 0.5)

Question 4

Reporting X^2

Answer 4

a #x# Chi Square test revealed proportion of something that did something differed by something, X^2 (DoF, N = #) = ###, p < ##

ex: a 3x2 Chi Square test revealed proportion of squirrels that chirped differed by fur color, X^2 (2, N = 891) = 42.3, p < .001

Question 5

What does Cramer’s V tell us?

Answer 5

• Effect size of X^2
• ranges from 0 to 1
• available in SPSS

Question 6

SPSS step 1: outer menus

Answer 6

Analyze > Descriptive Stats > Crosstabs

Question 7

SPSS step 2: ‘Statistics’ button

Answer 7

• Chi-square

- Phi and Cramer’s V

Question 8

SPSS step 3: ‘Cells’ button

Answer 8

Counts:
- observed
Percentages:
- row
- column
- total