Copyright 2013 © Limsoon Wong,
Why non-parametric methods
- The study variable generates data which are
scores and so should be treated as a categorical
variable with data measured on ordinal scale
- E.g., scoring system for degree of skin reaction to
a chemical agent:
- 1: intense skin reaction
- 2: less intense reaction
- 3: No reaction
- For such type of data, the assumption required
for parametric tests seem invalid => non-
parametric methods should be used
- Aka distribution-free tests, because they make no
assumption about the underlying distribution of
the study variables