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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