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