Table 1.

Description of various summary scores for expressing changes in HRQOL scores over time

Name	Formula	Description
AD	${\displaystyle Q_2-Q_1}$	Simple difference in the HRQOL between two time points. The mean of the AD values from all subjects corresponds to the Osoba’s MID (Osoba et al4).
pAD	${\displaystyle Q_{2c}-Q_{1c}}$	Applying AD per subgroup c=1 to 4, where c is based on baseline QOL values grouped as; 0–25, 26–50, 51–75 and 76–100.
RD1 – ordered	${\displaystyle \frac{Q_2-Q_1}{Q_1}\times 100}$	Per cent change from previous value.
RD2 – sum	${\displaystyle \frac{Q_2-Q_1}{Q_2+Q_1}}$	Per cent change compared with sum. Convention: if Q2=Q1=0 then RD2=0.
RD3 – baseline	${\displaystyle \frac{Q_2-Q_1}{Q_B}}$	Per cent change compared to baseline value (Q B).
Fixed value	${\displaystyle Q_2}$	MID is dependent on the observed value. This will result in a fixed threshold, not dependent on change in HRQOL score from previous value.
Slope	${\displaystyle \frac{Q_2-Q_1}{T_2-T_1}}$	The absolute difference between two time points is weighted by the corresponding time period.

Q_x, HRQOL outcome at time point T_x.

AD, absolute difference; HRQOL, health-related quality of life; MID, minimally important difference; pAD, piecewise absolute difference; RD, relative difference; RS, raw scores; QOL, quality of life.