Table 3. Rates of improvements (ROI) for YYIR1 of the different performance groups over a 2- and 4-year period. 2-year follow-up PG Formula ROI Linear Regression Benchmark ROI Mean (1823m – 1319m) / 2 252 m/y y = 252 x + 1112 Target ROI Low (1823m – 886m) /2 469 m/y Average (1823m – 1357m) / 2 233 m/y High (1823m – 1714m) / 2 55 m/y Attained ROI Low (1411m – 886m) /2 212 m/y y = 263 x + 696 Average (1920m – 1357m) / 2 252 m/y y = 252 x + 1112 High (2137m – 1714m) /2 263 m/y y = 212 x + 1503 4-year follow-up PG Formula ROI Linear Regression Benchmark ROI Mean (2175m – 1090m) / 4 271 m/y y = 543 x + 586 Target ROI Low (2175m – 703m) / 4 368 m/y Average (2175m – 1063m) / 4 278 m/y High (2175m – 1503m) / 4 168 m/y Attained ROI Low (2126m – 703m) / 4 356 m/y y = 712 x + 82 Average (1966m – 1063m) / 4 226 m/y y = 452 x + 568 High (2434m – 1503m) / 4 233 m/y y = 466 x + 1107 PG = Performance group; ROI = Rate of improvement; m/y = meter per year