Rangkorrelationen
Rangkorrelationen, often referred to in English as rank correlation, is a statistical measure used to assess the degree of association between two quantitative variables based on the order, or rank, of the observations rather than their raw values. Unlike conventional correlation coefficients such as Pearson’s r, rank correlation is non‑parametric and thus robust to outliers and to non‑linear monotonic relationships. It is particularly useful when the underlying distribution of the data is unknown, when the relationship is not expected to be linear, or when only ordinal information is available.
The most common rank‑correlation coefficient is Spearman’s rank‑order correlation, denoted by ρ (rho). It is computed by
Both τ (tau) and ρ (rho) take values between −1 and +1. A value of +1 indicates perfect
In practice, rank correlation is applied across many scientific domains: ecological studies often use it to