The defining relationship: T2DM is the clinical end-stage of insulin resistance. HOMA-IR scores above approximately 2.5 indicate clinically significant insulin resistance; once beta-cell exhaustion follows, diagnosed T2DM results. The r values here (0.97–0.98) approach the maximum possible for ecological data, because these two measures are not merely correlated — they are sequential stages of the same physiological process. A HOMA-IR test will typically detect insulin resistance 10–20 years before T2DM diagnosis — the critical reversible window that conventional medicine largely misses.