Transform compositional data (mole/mass fractions, GC compositions, sulfur speciation) using log-ratio transforms (clr, alr, ilr) and sequential binary partition (SBP)-based balances so regressions, PCA, and correlations are valid on the simplex. Use when analysing GC composition trends, sulfur-species splits, or any data that lives on the simplex. Don't use for ordinary numeric data, for compositional data where one component dominates and the rest are noise, or as a substitute for domain-specific physical models.
