Mean deviation equals the average absolute deviation from the center.
Key Concepts
- Concept: Mean absolute deviation
- Concept: Center: mean μ or x̄
- Concept: Absolute deviations: |x_i − center|
Steps
- Action: Choose center (mean μ or x̄)
- Action: Compute |x_i − center| for all i
- Action: Average: MD = (1/n) Σ |x_i − center|
Formula
$$text{MAD} = frac{1}{n} sum_{i=1}^{n} left| x_i – bar{x} right|$$
Population version: $$text{MAD}_{pop} = frac{1}{N} sum_{i=1}^{N} left| x_i – mu right|$$
General center a: $$text{MAD}(a) = frac{1}{n} sum_{i=1}^{n} left| x_i – a right|$$
Relation to normal distribution (optional): $$text{MAD} = sigma,sqrt{frac{2}{pi}} quad text{(for } X sim N(mu,sigma^2) text{)}$$
Example: For x = [2, 4, 6, 8], mean is 5; MAD = (|−3|+|−1|+|1|+|3|)/4 = 2.