Standardizing disease-specific quality of life measures across multiple chronic conditions: development and initial evaluation of the QOL Disease Impact Scale (QDIS®)

Table 4 Comparison of QDIS-7 means and reliability estimates, five disease groups

Disease	Mean (SD)^a	% with IRT Reliability ≥0.90 by Severity Level^b				Alpha^c	Test-retest reliability^d
Disease	Mean (SD)^a	Mild	Moderate	Severe	Total	Alpha^c	Test-retest reliability^d
Arthritis	54.24 (8.72)	(N = 718)	(N = 587)	(N = 231)	(N = 1536)	.94	.88
Arthritis	54.24 (8.72)	60.5	93.5	95.7	78.4	.94	.88
CKD	48.97 (9.17)	(N = 200)	(N = 61)	(N = 36)	(N = 297)	.94	.91
CKD	48.97 (9.17)	34.5	82.0	94.4	51.5	.94	.91
Cardiovascular	51.65 (9.87)	(N = 483)	(N = 112)	(N = 36)	(N = 631)	.94	.90
Cardiovascular	51.65 (9.87)	55.5	95.5	91.7	64.7	.94	.90
Diabetes	47.60 (7.75)	(N = 921)	(N = 329)	(N = 63)	(N = 1313)	.91	.83
Diabetes	47.60 (7.75)	38.6	72.0	100.0	49.9	.91	.83
Respiratory	48.45 (9.45)	(N = 1152)	(N = 306)	(N = 112)	(N = 1570)	.94	.88
Respiratory	48.45 (9.45)	36.4	87.3	93.8	50.4	.94	.88

Abbreviations: CKD chronic kidney disease
^aAnalysis of variance indicated that QDIS-7 group means differed across disease groups (F_(4,5413) = 152.1, p < 0.0001). QDIS-7 scores have mean = 50, SD = 10 in chronically-ill US general population; higher scores equal worse health
^bPercent with IRT estimated reliability ≥0.90. Severity defined as Mild (None, Mild), Moderate, or Severe (Severe, Very Severe) in response to item How would you rate the severity of your < condition > in the past 4 weeks?
^cInternal consistency reliability for arthritis (N = 1113), CKD (N = 261), cardiovascular (N = 578), diabetes (N = 857) and respiratory groups (N = 1156)
^dIntraclass correlation coefficient (ICC_(3,1)) for arthritis (N = 109), CKD (N = 37), cardiovascular (N = 63), diabetes (N = 75) and respiratory groups (N = 92)

ISSN: 1477-7525