Table 2.

Estimates of transition probabilities and 95% CI for sites that were healthy at 6 months based on CAL + BOP and PD + BOP classifications. States 1, 2 and 3 correspond to health, gingivitis and chronic periodontitis respectively. There was a 12% chance that a site that was healthy would convert to gingivitis (1 → 2) in the first 2 years for both CAL + BOP and PD + BOP classified models. The probabilities for progression to chronic periodontitis from healthy (1 →3) were at least three times higher for the CAL + BOP model compared to the PD + CAL model. After 2 years, recovery from gingivitis (2 → 1) was estimated as 75% for the CAL + BOP model and 83% for the PD + BOP model. Transitions 3 → 1 and 3 → 2 were not permissible.

	Predicted transition probabilities for sites that were healthy at 6 months
State transitions	CAL + BOP classified model		PD + BOP classified model
	Year 1	Year 2	Year 1	Year 2
1 → 2	0.12 (0.11,0.13)	0.12 (0.11,0.14)	0.12 (0.11,0.13)	0.12 (0.11,0.13)
1 → 3	0.05 (0.04, 0.06)	0.10 (0.08, 0.12)	0.01 (0.01,0.02)	0.03 (0.02, 0.04)
2 → 1	0.72 (0.68, 0.77)	0.75 (0.72, 0.78)	0.80 (0.77, 0.83)	0.83 (0.80, 0.85)
2 → 3	0.07 (0.04, 0.10)	0.12 (0.09, 0.15)	0.03 (0.01,0.05)	0.05 (0.02, 0.08)