3 - Categorical data analysis

Question 1

What is a nominal scale?

Answer 1

numbers serve as “tags” or “labels” only, to identify or classify an object
the number have no value

Question 2

What is the Chi-square test (χ2) used for

Answer 2

Used for counts and classifications of things on nominal scales
e.g. colour, species, habitats

Question 3

What are you checking for in Chi-square test?

Answer 3

frequencies we observe are compared with those we expect on the basis of a Null Hypothesis

If there is a difference between the 2 values -

1. calculated test statistic will exceed the critical value at the appropriate degrees of freedoms
2. reject the null hypothesis in favour of some alternative explanation

Question 4

How are expected frequencies derived?

Answer 4

Frequencies can be derived from:
The sample data
Or they are defined according to a Model.

Question 5

What are the 4 assumptions for Chi-square test?

Answer 5

1. Random sampling
2. Independent observations
3. Variable categories are mutually exclusive
4. Expected counts (none n < 1, 80% n > 5)