RELIABILITY AND VALIDITY
Internal Consistency Reliability.
Internal consistency reliability for the QLI (total scale) was supported by Cronbach's alphas ranging from .73 to .99 across 48 studies (Table 1). Cronbach's alphas for the four subscales have been published in 24 studies, which have provided support for internal consistency of the subscales (Table 2). Alphas ranged from .70 to .94 for the health and functioning subscale, and from .78 to .96 for the psychological/spiritual subscale. For the social and economic subscale, alphas were acceptably high 23 studies, ranging from .71 to .92. For the family subscale, alphas were acceptably high in 19 studies, ranging from .63 to .92.
Temporal (Stability) Reliability
For the total scale, support for temporal reliability was provided by test-retest correlations of .87 with a two-week interval and .81 with a one-month interval (Ferrans & Powers, 1985) and by correlations of .78 with a three to four-week interval (Rustoen et al.,1999). Temporal reliability also was supported by test-retest correlations with a two-week interval for all five scores: overall quality of life (r = .79), health and functioning (r = .72), social and economic (r =.68), psychological/spiritual (r = .76), and family (r = .69) (Dougherty et al., 1998).
Validity
Content Validity
Content validity of the QLI was supported by the fact that items were based both on an extensive literature review of issues related to quality of life and on the reports of patients regarding the quality of their lives (Ferrans & Powers, 1985). Support for content validity also was provided by an acceptably high rating using the Content Validity Index (Oleson, 1990).
Construct Validity
Convergent validity of the QLI was supported by strong correlations between the overall (total) QLI score and Campbell, Converse, and Rodgers (1976) measure of life satisfaction (r = .61, .65, .75, .77, .80, .83, .93) (Bliley & Ferrans, 1993; Ferrans & Powers, 1985; Ferrans & Powers, 1992; Anderson & Ferrans, 1997; Ferrans, 1990).
Further evidence for construct validity was provided by factor analysis. Factor analysis revealed four dimensions underlying the QLI: health and functioning, social and economic, psychological/spiritual, and family. The factor analytic solution explained 91% of the total variance. Factor analysis of the four primary factors revealed one higher order factor, which represented quality of life (Ferrans & Powers, 1992). Rannestad et al. (2000) subsequently performed factor analysis with a group of 284 Norwegian women, which supported the original four factors.
Construct validity also was supported using the contrasted groups approach. Subjects were divided into groups on the basis of self-reported levels of pain, depression, and success in coping with stress. Subjects who had less pain, less depression, or who were coping better with stress had significantly higher overall (total) QLI scores (Ferrans, 1990). The contrasted groups approach also was used to assess the construct validity of the social and economic subscale. It was found that those who had higher incomes had significantly higher quality of life scores on the social and economic subscale (Ferrans & Powers, 1992).
Sensitivity to Change/Responsiveness
Responsiveness to change (sensitivity) of the QLI has been demonstrated in 27 published intervention studies. In these studies, QLI scores changed significantly over time, when compared before and after an experimental intervention or therapeutic treatment (Table 3).
Table 1. Internal Consistency Reliability of the Ferrans and Powers Quality of Life Index (QLI): Total Scale |
Population |
Alpha |
Study |
Cancer |
Breast cancer patients
- Before treatment
- After treatment (8 weeks)
|
.93
.96
|
Hughes, 1993 |
Breast cancer surviors |
.95 |
Ferrans, 1990 |
Breast cancer survivors (younger) |
.95 |
Sammarco, 2003a |
Breast cancer survivors (older) |
.97 |
Sammarco, 2003b |
Breast cancer – mastectomy |
.88 |
Xiaokun, 2002 |
Melanoma patients |
.95 |
Cowan et al., 1992 |
Newly diagnosed patients |
.93, .95 |
Rustoen et al., 1999 |
Stem cell transplantation |
.87 |
Hacker et al., 2006 |
Thyroid cancer patients |
.96 |
Huang et al., 2004 |
|
Cardiac |
Angina pectoris (stable) patients |
.93 |
Dougherty et al., 1998 |
Angiogram patients |
.92 |
Delunas & Potempa, 1999 |
Angioplasty patients
- Before PTCA
- After PTCA (4-6 weeks)
|
.86
.96
|
Bliley & Ferrans, 1993 |
Angioplasty and bypass patients |
.98 |
Papadantonaki et al., 1994 |
Arrythmias (life-threatening) |
.98 |
Carroll et al., 1999 |
Cardiac rehabilitation |
.92 |
Deshotels et al., 1995 |
Coronary artery bypass (women)
- Before surgery
- Aftery surgery (3 months)
|
.91
.95
|
Penckofer et al., 2005 |
Heart Failure (end stage) |
.96 |
Scott, 2000 |
Heart failure |
.89 |
Scott et al., 2004 |
Implanted defibrillator |
.86 |
Carroll et al.. 2005 |
|
Caregivers |
Caregivers |
.92 |
Scott, 2000 |
Caregivers |
.93 |
Smith, 1999 |
|
Diabetes |
Diabetes (adults) |
.94 |
DeSouza & Nairy, 2003 |
Diabetes (adults) |
.97 |
Ozer & Efe, 2006 |
|
|
|
End Stage Renal Disease |
Hemodialysis and CAPD patients |
.90 |
Ferrans & Powers, 1985 |
Hemodialysis patients |
.93 |
Ferrans & Powers, 1992 |
Hemodialysis patients |
.88 |
Tsay & Healstead, 2002 |
|
|
|
HIV Positive/AIDS |
HIV+ |
.89 |
Nunes et al., 1995 |
HIV+ |
.84 |
Mellors et al., 1997 |
HIV+/AIDS |
.98 |
Yang et al., 2003 |
|
Parenteral Nutrition |
Parenteral nutrition |
.92 |
Smith et al., 2003 |
Parenteral nutrition |
.89 |
Smith, 1999 |
|
Stroke |
Stroke survivors |
.91 |
King, 1996 |
Stroke survivors
- 1 mo poststroke
- 6 mo poststroke
|
.73
.76
|
Robinson-Smith et al., 2000 |
|
|
|
Other Illness Groups |
Alzheimer's disease |
.92 |
Katsuno, 2003 |
Antibody deficiency |
.81 |
Sigstad et al., 2005 |
Chronic fatigue syndrome |
.93 |
Anderson & Ferrans, 1997 |
Chronic pain patients |
.96 |
All et al., 2000 |
Gynecological disorders |
.86, .94 |
Rannestad et al., 2000 |
Hip fracture |
.84 |
Johansson et al., 2002 |
Hospitalized patients |
.92 |
Larrabee et al., 2004 |
Intensive care patients (elderly) |
.96 |
Kleinpell & Ferrans, 2002 |
Multiple sclerosis patients |
.87 |
Stuifbergen, 1995 |
Nursing home residents |
.91 |
Tseng & Wang, 2001 |
Venous ulcers |
.99 |
Yamada et al., 2005 |
|
|
|
General Population |
Graduate students |
.93 |
Ferrans & Powers, 1985 |
Korean-American women |
.95 |
Kim & Rew, 1994 |
Older women |
.92 |
Nesbitt & Heidrich, 2000 |
Pregnant and postpartum women |
.96, .89 |
Canaval et al., 2000 |
|
|
|
Table 2. Internal Consistency Reliability of the Ferrans and Powers Quality of Life Index (QLI): Subscales |
Population |
Health and Functioning Subscale |
Social & Economic Subscale |
Psychological/ Spiritual Subscale |
Family Subscale |
Study |
Cancer |
Breast cancer survivors |
.90 |
.84 |
.93 |
.66 |
Ferrans, 1990 |
Breast cancer survivors (younger) |
.86 |
.81 |
.96 |
.82 |
Sammarco, 2003 a |
Breast cancer survivors (older) |
.88 |
.78 |
.90 |
.79 |
Sammarco, 2003 b |
Breast cancer – mastectomy |
.78 |
.85 |
.78 |
.82 |
Xiaokun, 2002 |
Melanoma Patients |
.92 |
.88 |
.85 |
.83 |
Cowan et al., 1992 |
Newly diagnosed patients |
.88 |
.82 |
.82 |
.79 |
Rustoen et al., 1999b |
Stem cell transplantation |
.77 |
.71 |
.77 |
.18 |
Hacker et al., 2006 |
Thyroid cancer patients |
.87 |
.85 |
.93 |
.73 |
Huang et al., 2004 |
|
Cardiac |
Angina pectoris (stable) |
.89 |
.78 |
.88 |
.70 |
Dougherty et al., 1998 |
Angioplasty and bypass |
.90 |
.89 |
.90 |
.79 |
Papapantonaki et al., 1994 |
Angioplasty and bypass |
.93 |
.87 |
.90 |
.76 |
Skaggs & Yates, 1999 |
Arrythmias (life-threatening) |
.93 |
.82 |
.90 |
.79 |
Carroll et al., 1999 |
Cardiac rehabilitation |
.87 |
.73 |
.88 |
.63 |
Deshotels et al., 1995 |
Implanted defibrillator |
.84 |
.52 |
.85 |
.79 |
Carroll et al.. 2005 |
|
Diabetes |
Diabetes (adults) |
.93 |
.88 |
.89 |
.85 |
Ozer & Efe, 2006 |
|
End-Stage Renal Disease |
Hemodialysis patients |
.87 |
.82 |
.90 |
.77 |
Ferrans & Powers, 1992 |
|
Other Illness Groups |
Alzheimer's disease |
.81 |
.87 |
.78 |
.48 |
Katsuno, 2003 |
Chronic fatigue syndrome |
.70 |
.84 |
.86 |
.70 |
Anderson & Ferrans, 1997 |
Chronic Pain |
.90 |
.92 |
.89 |
.72 |
All et al., 2000 |
HIV+ |
.84 |
.85 |
.80 |
.92 |
Nunes et al., 1995 |
Intensive care patients (elderly) |
.94 |
.83 |
.92 |
.79 |
Kleinpell & Ferrans, 2002 |
Stroke survivors |
.86 |
.77 |
.83 |
.32 |
King, 1996 |
|
|
|
|
|
|
General Population |
Pregnant women |
.83 |
.82 |
.82 |
.55 |
Canaval et al., 2000 |
Postpartum women |
.83 |
.71 |
.82 |
.47 |
Canaval et al., 2000 |
|
Table 3. Intervention Studies Demonstrating Sensitivity to Change/Responsiveness |
Population |
Type of Intervention |
Study |
Cardiac |
Angina pectoris |
External counterpulsation |
Aurora, et al. (1998) |
Angina pectoris |
External counterpulsation |
Aurora et al. (2002) |
Angina pectoris |
Angina medications (comparison) |
Dougherty, et al. (1998) |
Atrial Fibrillation |
Ablation/pacemaker implantation |
Jenkins et al. (1996) |
Atrial Fibrillation |
Antiarrhythmics vs. implantable defibrillators |
Jenkins et al. (1997) |
Atrial fibrillation |
Rate vs. rhythm-control |
AFFIRM investigators (2005) |
Atrial fibrillation |
Implantable defibrillator |
Hamilton & Carroll (2004 |
Coronary artery disease |
Coronary angioplasty |
Bliley & Ferrans (1993) |
Coronary artery disease |
Coronary angioplasty |
Faris & Stotts (1990) |
Coronary artery disease |
Cardiac bypass surgery |
Kolz (1989) |
End stage cardiac disease |
Heart transplantation |
Grady et al. (1993) |
Heart disease |
Cardiac rehabilitation |
McEntree & Badenhop (2000) |
Heart disease |
Cardiac rehabilitation |
Verrill et al. (2001) |
Heart failure |
Educational (goals and support) |
Scott et al., 2004 |
Valvular heart disease |
Balloon valvoplasty |
Hixon (1992) |
|
Diabetes |
Diabetes (adults) |
Educational intervention |
DeSouza & Nairy, 2003 |
Diabetes (adults) |
Kidney and pancreas-kidney allografts |
Hathaway et al. (1994; 1994) |
|
|
|
End Stage Renal Disease |
Kidney failure (end stage) |
Kidney transplantation |
Hathaway et al. (1992) |
Kidney failure (end stage) |
Kidney transplantation |
Johnson et al. (1998) |
|
Lung Disease |
Lung Disease |
Pulmonary rehabilitation |
McEntee & Badenhop (2000) |
Lung disease |
Pulmonary rehabilitation |
Verrill et al., 2005 |
|
|
|
Other Illness Groups |
Chronic fatigue syndrome |
Rehabilitation program |
Taylor, 2004 |
Critically ill |
Care in high dependency unit |
Brooks (2000) |
Liver disease (end stage) |
Liver transplantation |
LoBiondio-Wood et al. (1997) |
Neutropenia |
Granulocyte colony stimulating factor |
Fazio & Glasy (1991) |
Parenteral nutrition |
Educational intervention |
Smith et al., 2003 |
Stroke survivors |
Stroke rehabilitation |
Robinson-Smith et al., 2000 |
REFERENCES
Complete reference citations are provided on this website in the section entitled, “Published QLI Research”.
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