Behavioral Research: Statistical Methods

**Correlation is not causation** — memorise this once and for all. Two variables can correlate because (1) A causes B, (2) B causes A, (3) a third variable C causes both, or (4) coincidence. Showing co-movement establishes association, not causation. **Pearson r** measures linear association in $[-1, 1]$; **Spearman ρ** uses ranks and captures monotone (possibly nonlinear) associations and is robust to outliers; **partial correlation** isolates X-Y association after removing a third variable Z. Reliability is the *quantified* version of consistency from Unit 2 — Cohen's κ for inter-rater nominal, Cronbach's α for internal consistency.