Minimal detectable change for mobility and patient-reported tools in people with osteoarthritis awaiting arthroplasty

Table 3 Agreement and reliability indices of objective or patient-reported outcome measures

	Week 1 mean (sd)	Week 2 mean (sd)	Difference mean (sd)	SEM (95% CI)	90% confidence in score	MDC₉₀	MDC₉₅	CV%
Knee
6MWT (m) n = 72	344.9 (105.6)	348.4 (102.3)	-3.5 (40.3)	28.5 (24.5 to 34.1)	46.9	66.3	79.0	8
TUG* (s), n = 74	12.7 (4.7)	13.1 (5.4)	-0.4 (3.7)	NA	NA	±30.8%	±36.7%	13
VAS Pain (cm), n = 71	6.8 (2.0)	6.8 (1.9)	0.1 (1.6)	1.0 (0.9 to 1.2)	1.7	2.4	2.8	15
KOOS, n = 68
Pain	39.0 (18.7)	36.7 (18.2)	2.3 (10.3)	7.3 (6.2 to 8.8)	12.0	17.0	20.2	19
Symptoms	38.8 (19.2)	39.1 (18.8)	-0.4 (12.3)	8.7 (7.4 to 10.5)	40.0	20.2	24.1	22
ADL	43.8 (18.6)	40.2 (19.1)	3.6 (10.6)#	7.5 (6.4 to 9.0)	12.3	17.4	20.8	17
QOL	21.7 (7.7)	23.8 (18.8)	-2.7 (13.8)	9.6 (8.2 to 11.6)	15.9	22.4	26.6	44
Hip
6MWT (m), n = 54	339.8 (107.8)	347.3 (105.3)	-7.5 (41.6)	29.4 (24.7 to 36.3)	57.7	68.5	81.5	9
TUG* ( s), n = 56	14.0 (7.2)	13.8 (6.6)	0.13 (3.6)	NA	NA	±37.5%	±44.6%	16
VAS Pain (cm), n = 58	7.1 (2.3)	6.8 (1.9)	0.4 (1.6)	1.2 (1.0 to 1.4)	1.9	2.7	3.3	17
HOOS, n = 56
Pain	36.0 (20.9)	34.4 (20.6)	1.6 (11.0)	7.8 (6.6 to 9.6)	12.8	18.1	21.6	22
Symptoms	42.7 (19.4)	38.1 (21.8)	4.6 (11.6)#	8.2 (6.9 to 10.1)	13.5	19.2	22.7	19
ADL	36.7 (20.9)	34.9 (19.7)	1.8 (9.0)	6.4 (5.4 to 7.8)	10.5	14.8	17.7	17
QOL	20.4 (20.2)	21.8 (21.6)	-1.4 (12.5)	8.8 (7.5 to 10.9)	14.6	20.6	24.4	43

Key: SEM, standard error of measurement with 95% confidence level; MDC₉₀ and MDC₉₅, minimal detectable change at the 90% and 95% confidence level; CV%, co-efficient of variation per cent; 6MWT, six-minute walk test; TUG, timed up-and-go; VAS, visual analogue scale; KOOS, Knee Injury and Osteoarthritis Outcome Score; HOOS, Hip Disability and Osteoarthritis Outcome Score; ADL, activities of daily living; QOL, quality of life; NA, not applicable (The SEM for TUG is not provided as it is not derived using the same formula due to its skewed distribution); *TUG data were log-transformed - the corresponding MDC₉₀ and MDC₉₅ are then interpreted as 90% and 95% of the measurements being within a ratio of the original measurement. Note, average Week 1 6MWT above slightly differs from average Week 1 reported for the comparison between practise and official Week 1 as people who did not have a practise test are included in the average for Week 1 above; #, significantly different, p < 0.05.

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