TABLE 3
Per cent total decline in forced vital capacity per cent predicted (FVCP) relative to the total range, and slope of decline at various key time points
| Time relative to NIPPV start (months) | Per cent total decline | FVCP in overall cohort | Change in FVCP/month in overall cohort | Change in FVCP/month (adherent) | Change in FVCP/month (nonadherent) |
| ∼30 | 0 | 74.0 | 0 | 0 | 0 |
| b3−b4 | 27 | 65.0 | −2.11 | −2.64 | −1.85 |
| b3 | 50 | 57.3 | −2.69 | −3.35 | −2.35 |
| b3+b4 | 73 | 49.6 | −2.11 | −2.64 | −1.85 |
| 0 | ≥85 | 45.9 | −1.43 | −1.50 | −1.17 |
| ∼20 | 100 | 40.6 | 0 | 0 | 0 |
b3: time (months) to the midpoint between the two asymptotes, also representing the inflection point of the FVCP time-course curve; b4: a timescale factor (months) that reflects the rapidity of decline of forced vital capacity, such that a smaller b4 reflects a more rapid decline.
Slopes are derived from the first derivative of vital capacity with time of the following equation: FVCP = b1 + b2/(1+e((b3−t)/b4)) such that 
.