Comprehensive introduction to correlation in psychology — scatter plots, direction and strength of association, Pearson r, Spearman Rho, Kendall Tau, and Chi-Square as measures of relationship for different data types.
Complete guide to Kendall's Tau (τ) — the non-parametric rank correlation for judge agreement, concordant/discordant pair logic, step-by-step calculation with and without ties, significance testing, and comparison with Spearman Rho.
Master Spearman's Rank Order Correlation (rho) and Kendall's Tau — nonparametric alternatives to Pearson's r for ordinal data, rank data, and situations where Pearson's assumptions are violated.