- Nominal (N): Categorical data with no logical order or ranking, used to label variables without quantitative value.
- Examples: Eye color, country names, gender.
- Operations: Counting, mode.
- Ordinal (O): Categorical data with a clear, inherent ordering or ranking, but the intervals between values are unknown or inconsistent.
- Examples: Survey responses (satisfied, neutral, dissatisfied), education level, race positions (1st, 2nd).
- Operations: Median, rank order.
- Interval (I): Numerical data where the distance between two values is meaningful and equal. The zero point is arbitrary, meaning it does not represent a complete absence of the value.
- Examples: Temperature in Celsius or Fahrenheit, time in 12-hour clock.
- Operations: Addition, subtraction, mean.
- Ratio (R): Numerical data that possesses all properties of interval data but includes a true, absolute zero point. The zero point implies the absence of the quantity.
- Examples: Weight, height, age, income.
- Operations: Multiplication, division, mean, median.
Key Characteristics
- Hierarchy: Each level includes the characteristics of the ones below it. Ratio is the most complex, while Nominal is the simplest.
- Qualitative vs. Quantitative: Nominal and Ordinal are typically categorical (qualitative), while Interval and Ratio are numerical (quantitative).
- Importance: Knowing the level of measurement helps determine the statistical tests and data visualization techniques to use.