Stroke Specific Quality of Life Scale (SS-QOL)

Evidence Reviewed as of before: 19-08-2008
Author(s): Lisa Zeltzer, MSc OT
Editor(s): Nicol Korner-Bitensky, PhD OT; Elissa Sitcoff, BA BSc

Purpose

The Stroke Specific Quality Of Life scale (SS-QOL) is a patient-centered outcome measure intended to provide an assessment of health-related quality of life (HRQOL) specific to patients with stroke.

In-Depth Review

Purpose of the measure

The Stroke Specific Quality Of Life scale (SS-QOL) is a patient-centered outcome measure intended to provide an assessment of health-related quality of life specific to patients with stroke.

Available versions

The SS-QOL was published and validated in 1999 by Williams, Weinberger, Harris, and Clark.

Features of the measure

Items:

Scale domains and items were derived from a series of interviews with post-stroke patients (Williams et al. 1999a).

Patients must respond to each question of the SS-QOL with reference to the past week. It is a self-report scale containing 49 items in 12 domains:

  • Mobility (6 items)
  • Energy (3 items)
  • Upper extremity function (5 items)
  • Work/productivity (3 items)
  • Mood (5 items)
  • Self-care (5 items)
  • Social roles (5 items)
  • Family roles (3 items)
  • Vision (3 items)
  • Language (5 items)
  • Thinking (3 items)
  • Personality (3 items)

Subscales:

Energy, Upper extremity function, Work/productivity, Mood, Self-care, Social roles, Family roles, Vision, Language, Thinking, and Personality.

Equipment:

Only a pencil and the test are needed.

Training:

No training is required, as the SS-QOL is intended to be self-administered. One study suggests that the scale can be administered to patients with stroke reliably over the telephone (Williams, Redmon, Saul & Weinberger, 2000).

Time:

It takes approximately 10-15 minutes to complete the SS-QOL scale.

Scoring:

Items are rated on a 5-point Likert scale. There are 3 different response sets (see table below). Patients must respond to each item using the corresponding response set as indicated on the scale (Williams et al. 1999a). For example, the item “did you have any trouble doing daily work around the house?” requires response set 2, which ranges from “couldn’t do it at all” to “no trouble at all”.

Response Sets:

1. Total help 2. A lot of help 3. Some help 4. A little help 5. No help needed
1. Couldn’t do it at all 2. A lot of trouble 3. Some trouble 4. A little trouble 5. No trouble at all
1. Strongly agree 2. Moderately agree 3. Neither agree nor disagree 4. Moderately disagree 5. Strongly disagree

Higher scores indicate better functioning. The SS-QOL yields both domain scores and an overall SS-QOL summary score. The domain scores are unweighted averages of the associated items while the summary score is an unweighted average of all twelve domain scores (Williams et al. 1999b).

Alternative forms of SS-QOL

  • The Stroke and Aphasia Quality Of Life Scale (SAQOL-39 – Hilari, Byng, Lamping, & Smith, 2003). Developed from the SS-QOL for use in patients with long-term aphasia, the SAQOL-39 has four subdomains (Physical, Psychosocial, Communication, and Energy). It is an interview-administered self-report scale. It is comprised of items from the SS-QOL that have been modified to ensure they are appropriate for use in individuals with aphasia. The SAQOL-39 has four additional items that were added to increase the content validity of the scale with this population. These four items focus on the difficulties with understanding speech, issues with decision-making, and the impact of language difficulties on family and social life.

Hilari et al. (2003) reported that the SAQOL-39 has good acceptability, adequate to excellent internal consistency (Cronbach’s alphas ranging from 0.74 to 0.94), excellent test-retest reliability (intraclass correlation coefficient = 0.89 to 0.98), and poor to excellent construct validity (corrected domain-total correlations, r = 0.38 to 0.58; convergent, r = 0.55 to 0.67; discriminant, r = 0.02 to 0.27 validity). Further research is needed to confirm its psychometric properties and to determine its appropriateness as a clinical outcome measure.

Client suitability

Can be used with:

  • Individuals with mild or moderate stroke.

Should not be used in:

  • Patients without stroke. The SS-QOL was developed and validated specifically for individuals with stroke and has been examined for use in this population only.
  • Severe stroke populations. The SS-QOL has not yet been tested among patients with severe stroke.
  • Should be used with caution in patients with aphasia. Although the modified version of the scale, the SAQOL-39, has been validated for use in patients with long-term aphasia, it is a relatively new measure that requires further psychometric testing.
  • Patients who require a proxy to complete. A study by Williams et al. (2006) compared proxy ratings of the SS-QOL to patient self administration in 225 patient-proxy pairs. Proxies rated all domains of SS-QOL lower than the patients. The intraclass correlation coefficient (ICC) for each domain ranged from poor (r = 30 for role function) to adequate (r = 0.59 for physical function). Proxy overall SS-QOL score was also rated lower than the patient score (3.7 versus 3.4) with an ICC of r = 0.41. It is recommended that information obtained from proxy respondents be treated as supplementary rather than substantive and that use of proxy be restricted to individuals either living with or in daily contact with the patient (Snow, Cook, Lin, Morgan & Magaziner, 2005; Muus, Petzold & Ringsberg, 2009).
  • For patients who require a proxy, the Stroke Impact Scale is a more reliable and valid measure of HRQOL (Duncan, Lai, Tyler, Perera, Reker, & Studenski, 2002).

In what languages is the measure available?

  • Danish (SS-QOL-DK): translated Muus & Ringsberg, 2005 and validated Muus, Williams & Ringesberg, 2007.
  • German: translated Ewart & Stucki, 2007 and initial validation study completed Ewart & Stucki, 2007. The initial validation study revealed validity of the total SS-QOL German score, however, some subscales (Energy, Mood and Thinking) were not validated. Further research is required.

Summary

What does the tool measure? Health related quality of life
What types of clients can the tool be used for? The SS-QOL was developed for use in patients with stroke.
Is this a screening or assessment tool? Assessment.
Time to administer Approximately 10-15 minutes to complete.
Versions The Stroke and Aphasia Quality Of Life Scale (SAQOL-39)
Other Languages Translated and validated in Danish. Translated in German.
Measurement Properties
Reliability

Internal consistency:

One study examined the internal consistency of the SS-QOL and found that the internal consistency ranged from adequate (for work/productivity subscale) to excellent (for self-care).

Test-retest:
One study examined the test-retest reliability of the SS-QOL and found excellent test-retest.

Inter-rater:
One study examined the inter-rater reliability of the SS-QOL and found excellent inter-rater.

Validity

Criterion:

Predictive:

The SS-QOL summary score significantly predicted overall post-stroke health-related quality of life.

Construct:

Convergent:

Most domains of the SS-QOL correlate with the Barthel Index, the Beck Depression Inventory, and subscales of the SF-36.

Floor/Ceiling Effects One study reported ceiling effects exceeding 20% in 10 out of 12 domains of the SS-QOL, and a floor effect of 24% in the Energy domain. Floor or ceiling effect exceeding 20% are typically considered poor.
Does the tool detect change in patients? One study found that the SS-QOL had only a moderate ability to detect change in patients between 1 and 3 months post-stroke. A subsequent study involving an alternative language version of the SS-QOL, found a small to moderate ability to detect change in patients between 3 and 12 month post-stroke. In a later study, the minimal clinically detectable difference for the mobility, self-care and upper extremity function subscales was defined as a mean change in score of at least 1.5, 1.2 and 1.2 respectively.
Acceptability Further investigation on the reliability, validity, and sensitivity of the SS-QOL is required with larger numbers of subjects. This measure has not been tested in severely affected patients with stroke. For patients with aphasia, the SAQOL-39 is a more suitable version of the measure, however, it is a relatively new measure, which requires further psychometric testing. The scale is not suitable for use by proxy.
Feasibility No training is required for the SS-QOL as the measure is intended to be completed by self-report. The measure is simple to score and is based on a 5-point Likert scale.
How to obtain the tool?

Click here to find a copy of the SS-QOL.

Psychometric Properties

Overview

The Stroke Specific Quality of Life Scale (SS-QOL) is a new scale and has not been well studied. It has not been tested among severe stroke populations. To our knowledge, the creators of the SS-QOL have personally gathered the majority of psychometric data that are currently published on the scale. Further investigation on the reliability, validity, and sensitivity of the SS-QOL is required with larger numbers of subjects.

Floor and Ceiling Effects

Czechowsky and Hill (2002) examined the SS-QOL and reported ceiling effects exceeding 20% in 10 out of 12 domains of the SS-QOL, and a ceiling effects exceeding 20% are typically considered poor.

Reliability

Internal consistency:

Williams et al. (1999a) examined the internal consistency of the SS-QOL in 34 individuals with stroke and found that Cronbach’s alpha ranged from adequate (alpha = 0.75 for work/productivity subscale) to excellent (alpha = 0.89 for self-care), suggesting that the SS-QOL has a strong internal consistency.

Test-retest:

In a study by Williams et al. (2000), the SS-QOL was administered by a trained interviewer to 47 stroke survivors at baseline and again within 2 hours of the initial interview. SS-QOL scores were highly correlated (r = 0.92), showing excellent test-retest reliability.

Inter-rater:

The SS-QOL was also administered by a trained interviewer to 24 stroke survivors and then a second trained interviewer re-administered the SS-QOL within 2 hours of the first interview. SS-QOL scores were highly correlated (r = 0.92), demonstrating excellent inter-rater reliability of the SS-QOL.

Validity

Criterion:

Predictive:

Williams et al. (1999b) administered the SS-QOL to a total of 71 patients 1-month post-ischemic stroke. Multivariate analysis showed that the SS-QOL summary score significantly predicted overall post-stroke health-related quality of life (HRQOL) (OR = 2.97). When scores were examined on the domain level, however, only one domain, Family Roles, was significantly different between groups, with higher scores in those patients with better overall HRQOL.

Construct:

Convergent:

Williams et al. (1999a) examined the validity of the SS-QOL in 34 survivors of stroke and reported that most domains of the SS-QOL correlated with the Barthel Index, Beck Depression Inventory, and subscales of the SF-36. The Energy, Family Roles, Mobility and Work/Productivity domains were significantly associated with corresponding subscales on the SF-36. Total SS-QOL score correlated excellently with the overall SF-36 health status rating (r = 0.65). The self-care domain was adequately correlated with the Barthel Index (r = 0.45). Upper Extremity Function showed a positive but poor relationship with the Barthel Index and the National Institutes of Health Stroke Scale Upper Extremity score (r = 0.18).

However, in this study, a few domains did not show a significant relationship with their corresponding measures. Scores in the Language and Thinking domains were not associated with selected items from the National Institutes of Health Stroke Scale (r = 0.00 and r = 0.10 respectively). This most likely occurred because patients with language and cognitive deficits were excluded, i.e., there were no patients with a score > 1 on these items. Furthermore, the SS-QOL Social Roles domain was not associated with the SF-36 Social Functioning subscale score (r = 0.01). Finally, the Vision domain of the SS-QOL did not correlate with the National Institutes of Health Stroke Scale Visual Field and Ocular Movement scores (r = 0.11).

Responsiveness

Williams et al. (1999a) examined the standardized effect size scores for the interval between 1 and 3 months post-stroke in 34 individuals with stroke. Effect sizes ranged from small (ES = 0.20 for the personality domain) to large (ES = 0.83 for the social roles domain). One half of the SS-QOL domains demonstrated less than moderate effect sizes. The ‘amount of help’ response set appeared to lack responsiveness. The results of this study demonstrate that the SS-QOL has only adequate responsiveness.

Muus et al. (2011) investigated the responsiveness of the Danish language version of the SS-QOL (SSQOL-DK). Patients were assessed at 3 and 12 months following stroke. Small standardized effect sizes were found for all domains (-0.03-0.40), except the social roles domain which demonstrated moderate standardized effect size (-0.53).

Lin, Fu, Wu & Hsieh (2011) examined the minimal clinically important difference (CID), of the mobility, self-care and upper extremity function subscales of the SS-QOL. The study included 74 patients with stroke receiving rehabilitation and the SS-QOL was administered at baseline and at 3 weeks. The MCID ranges for the mobility, self-care and upper extremity function subscales were 1.5 – 2.4, 1.2 – 1.9, and 1.2 – 1.8 respectively. The results of the study indicate that mean change of score on the mobility, self-care and upper extremity function subscale should reach 1.5, 1.2 and 1.2, respectively, in order for change to be interpreted as clinically meaningful.

References

  • Czechowsky, D., Hill, M. D. (2002). Neurological Outcome and Quality of Life after Stroke due to Vertebral Artery Dissection. Cerebrovascular Diseases, 13, 192-197.
  • Duncan, P. W., Lai, S. M., Tyler, D., Perera, S., Reker, D. M., Studenski, S. (2002). Evaluation of proxy responses to the Stroke Impact Scale. Stroke, 33, 2593-2599.
  • Ewart, T. & Stucki, G, (2007). Validity of the SS-QOL in Germany and in survivors of hemorrhagic or ischemic stroke. Neurorehabilitation and Neuro Repair, 21, 161-168.
  • Hilari, K., Byng, S., Lamping, D. L., Smith, S. C. (2003). Stroke and Aphasia Quality of Life Scale-39 (SAQOL-39): Evaluation of acceptability, reliability, and validity. Stroke, 34, 1944-1950.
  • Lin, K-C., Fu, T., Wu, C-Y. & Hsieh, C-J. (2011). Assessing the stroke-specific quality of life for outcomes measurement in stroke rehabilitation: Minimal detectable change and clinically important difference. Health and Quality of Life Outcomes, 9, 5. Retrieved April 25, 2012 from Sage Journals database.
  • Muus, I., Christensen, D., Petzold, M., Harder, I., Johnsen, S.P., Kirkevold, M., Ringsberg, K.C. (2011). Responsiveness and sensitivity of the Stroke Specific Quality of Life Danish version. Disability and Rehabilitation, 33(25-26), 2425-2433.
  • Muus, I., Petzold, M. & Ringsberg, K.C. (2009). Health-related quality of life after stroke: Reliability of proxy responses. Clinical Nursing Research, 18(2), 103-118.
  • Muus, I., Ringsberg, K. C. (2005). Stroke Specific Quality of Life Scale: Danish adaptation and a pilot study for testing psychometric properties. Scand J Caring Sci, 19, 140-147.
  • Muus, I., Williams, L.S. & Ringsberg, K.C. (2007). Validation of the Stroke Specific Quality of Life Scale (SS-QOL): Test of reliability and validity of the Danish version (SS-QOL-DK). Clinical Rehabilitation, 21, 620-627.
  • Snow, A.L., Cook, K.F., Lin, P.S., Morgan, R.O. & Magaziner, J. (2005). Proxies and other external raters: Methodological considerations. Health Services Research, 40(5), 1976-1693.
  • Williams, L. S., Weinberger, M., Harris, L. E., Clark, D. O., Biller, J. (1999a). Development of a stroke-specific quality of life scale. Stroke, 30(7), 1362-1369.
  • Williams, L. S., Weinberger, M., Harris, L. E., Biller, J. (1999b). Measuring quality of life in a way that is meaningful to stroke patients. Neurology, 53, 1839-1843.
  • Williams, L. S., Redmon, G., Saul, D. C., Weinberger, M. (2000). Reliability and telephone validity of the Stroke-specific Quality of Life (SS-QOL) scale. Stroke, 32, 339-b.
  • Williams, L. S., Bakas, T., Brizendine, E., Plue, L., Tu, W., Hendrie, H., Kroenke, K. (2006). How valid are family proxy assessments of stroke patients’ health-related quality of life? Stroke, 37, 2081-2085.

See The Measure

Please click here for a copy of the Stroke-Specific-Quality-of-Life-Scale (SS-QOL).

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