Department of Psychiatry, University of Liverpool, Royal Liverpool Hospital, Liverpool
Department of Neuropsychology, University of Liverpool, Royal Liverpool Hospital
Oxford Outcomes, Headington, Oxford
Janssen-Cilag Ltd, High Wycombe
Outcomes Research, Janssen-Cilag Ltd, High Wycombe
Department of Psychiatry, University of Liverpool, Royal Liverpool Hospital
Nuffield College, Oxford
Health Services Research Unit, University of Oxford, Institute of Health Sciences, Headington, Oxford
Correspondence: Professor Greg Wilkinson, University Department of Psychiatry, Royal Liverpool University Hospital, Prescot Street, Liverpool L69 3BX
Declaration of interest Janssen-Cilag Ltd funded the project. G.W. is Editor of The British Journal of Psychiatry.
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aims To develop and validate a short, self-report quality of life questionnaire (the Schizophrenia Quality of Life Scale, SQLS).
Method People with schizophrenia in Liverpool were recruited via the NHS. Items, generated from in-depth interviews, were developed into an 80-item self-report questionnaire. Data were factor analysed, and a shorter form measure was tested for reliability and validity. This measure was administered together with other self-report measures - SF-36, GHQ-12 and HADS - to assess validity.
Results Data were analysed to produce a final 30-item questionnaire, comprising three scales (psychosocial, motivation and energy, and symptoms and side-effects) addressing different SQLS dimensions. Internal consistency reliability of the scale was found to be satisfactory. There was a high level of association with relevant SF-36, GHQ-12 and HADS scores.
Conclusions The SQLS was completed within 5-10 minutes. It possesses internal reliability and construct validity, and promises to be a useful tool for the evaluation of new treatment regimes for people with schizophrenia.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
What is lacking for research and clinical purposes is a practical, brief self-report measure, developed according to standardised methodology and possessing good psychometric properties. To fill this gap, we present the results of a study illustrating the development and validation of a novel QoL measure specific to people with schizophrenia : the Schizophrenia Quality of Life Scale (SQLS).
![]() |
METHOD |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Subjects and procedures
Stage I : Item generation
Exploratory in-depth semi-structured interviews with 20 patients (male and
female) with schizophrenia were tape-recorded and generated 378 candidate
items. (The interview schedule is available from the first author upon
request.) The sample size for this stage of the study was determined by the
point at which no new significant themes emerged from the interviews.
People diagnosed with schizophrenia were randomly selected from two general practitioner lists. They were contacted by letter and those who agreed to take part were interviewed by one of the research team (B.H.). Each was asked to describe areas of life that had been influenced by their condition, and a list of these aspects was extracted from the transcribed interviews. Six researchers, including a psychiatrist and psychologists, then idependently devised questionnaire items from this list. These were discussed jointly, scrutinised for repetition and ambiguity, and a final set of items was agreed by consensus. This gave a final pool of 87 items, which were drafted into a questionnaire asking about the QoL of patients over the past 7 days. (The full item pool and a list of items changed are available from the first author upon request.) The eliminated items were : "I enjoy looking after myself", "People are frightened by the way I am", "I have enough money", "I take drugs so that I can cope", "I can accept my limitations", "I feel like I fit in" and "People understand me" ; "I am concerned about my sex drive" and "My sex drive has declined" were combined to give "I am concerned about my sex life".
A pilot study was undertaken on 20 people with schizophrenia recruited using the same approach. The patients were asked six open-ended questions after completing the questionnaire (responses available from the first author upon request) :
As a result, seven items were removed at this stage, as patients thought them ambiguous or meaningless.
The face validity of the questionnaire was agreed at this stage by a psychiatrist (G.W.), in informal consultation with psychiatrist colleagues. Consequently a long-form questionnaire was devised containing 80 items. Respondents could select a response to each question from : Never (0) ; Rarely (1), Sometimes (2), Often (3), or Always (4).
Stage 2 : Item reduction and scale generation
This phase enabled the development of a shorter and more practical
instrument, and the identification of three scales addressing different
dimensions of the impact of schizophrenia on quality of life.
The 80-item questionnaire was completed by individuals with schizophrenia in contact with secondary care clinics : 229 people were approached and 161 (70%) agreed to take part. The mean age of respondents was 43 years (s.d.=11.3 ; min=17, max=73, n=158 ; age of two respondents not known) ; 105 (65%) were male and 56 (35%) female ; 54 (34%) were living alone, and the remainder were living with friends or relatives.
State 3 : Testing construct validity
Statistical procedures were undertaken (documented below) to reduce the
number of items and to devise a short-form instrument. The construct validity
of the resulting measure was assessed by comparing results on the SQLS with
those from established measures of health status (SF-36) and psychological
outcome (the General Health Questionnaire (GHQ) and Hospital Anxiety and
Depression Scale (HADS)).
The SQLS was administered with the SF-36, GHQ-12 (Goldberg & Williams, 1988) and HADS (Zigmond & Snaith, 1983) in both clinic and home-based settings. Of the 112 people with schizophrenia who were approached, 78 (70%) agreed to take part. The mean age of patients was 40 years (s.d.=11.9 ; min=18 ; max=64, n=78) ; 25 (32%) lived alone, and the remainder lived with friends or relatives.
The SQLS was completed by almost all respondents within 5-10 minutes. The few who took longer expressed the need to think longer about their responses.
Statistical procedures
Principal components analysis was carried out on results from the 161
questionnaires obtained in Stage 2 to reduce the number of items and determine
the dimensions underlying the remaining items. Internal reliability was
assessed using Cronbach's
(Cronbach, 1951). Items were
summed for each dimension and transformed onto a scale from 0 (best health
status) to 100 (worst health status). Summary statistics were provided in the
form of means, standard deviations and quartiles. Construct validity was
assessed correlating results on the SQLS with other measures using the
Spearman correlation coefficient, indicating the spread of responses and the
lack of floor/ceiling effects.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Item reduction and scale generation
A principal components analysis was carried out on results from the 161
questionnaires obtained in Stage 2. The detailed results are available from
the first author upon request. All questionnaires were scored using a
Likert-type format. Three factors with item-loading 0.5 were identified,
which appeared to characterise three underlying constructs : psychosocial,
motivation and energy and symptoms and side-effects. These three factors,
which accounted for 40.6% of the variance, were then subjected to varimax
rotation. Items loading <0.4 on any factor were removed at this stage. It
was assumed that items loading
0.4 on each factor constituted a scale.
Internal reliability was assessed on the items constituting each scale. Items
were removed from each of the scales if they increased the
coefficient.
These procedures resulted in a set of 30 items incorporated in three scales :
Transformation of scale scores
The purpose of the three scales is to indicate the extent of difficulty on
each domain measured. Consequently, each scale score is transformed to have a
range from 0 (the best status as measured on the SQLS) to 100 (the worst
status as measured on the SQLS), with each scale calculated as follows : the
scale score (SS) equals the total of raw scores of each item in the
scale (RStot), divided by the maximum possible raw score
of all the items in the scale (RSmax), all multiplied by
100 : SS=(RStot/RSmax)
x 100. Table 1 shows the
three scale scores for the sample as a whole and the distribution of the
scores, indicating no floor/ceiling effects. The principal components analysis
is available from the first author upon request.
|
Internal consistency
Table 2 shows the
correlations of items with their scale totals, and the internal consistency
reliability of the scales (that is, the extent to which items in a scale
reflect a single underlying dimension). Items were highly correlated with
their own scale score (corrected to exclude the item being correlated).
Internal reliability was assessed using Cronbach's
(1951) statistic. All
the scales show good internal consistency reliability
(Nunnally & Bernstein,
1994 ; Ware et al,
1994). We consider that if the
value is too high, this may
suggest a high level of item redundancy, that is a number of items asking the
same question, but in slightly different ways
(Hattie, 1985 ;
Boyle, 1991) and may indicate
that some of the items are unnecessary. Nunnally
(1978) suggests that
should be above 0.70, but probably not higher than 0.90.
|
Construct validity
Construct validity was assessed comparing results on the SF-36, GHQ-12 and
HADS. We hypothesised that the SF-36 energy dimension would be strongly
associated with SQLS motivation and energy dimension, and that the SF-36
mental health scores would be strongly associated with the psychosocial
score of the SQLS. These predicted correlations were substantiated (SF-36
energy correlation with SQLS motivation and energy : =0.72,
P<0.001, n=76 ; SF-36 mental health correlation with
SQLS psychosocial :
=0.65, P<0.001, n=75). It was
hypothesised that significant correlations between scores would be found for
the GHQ-12 and HADS with all dimensions of the SQLS. These hypothesised
associations were indeed found (see Table
3).
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We believe that a measure cannot be classified as measuring QoL unless that measure is subjective : QoL is commonly defined as "a multidimensional concept based on patients' self-report about their quality of life" (Awad et al, 1997). There is an untested assumption that people with schizophrenia cannot reliably complete self-report questionnaires, but there is growing empirical support for the use of short self-administered instruments with this group. Data suggest that a brief, self-administered QoL measure can yield results consistent with in-depth interviews (Greenley & Greenberg, 1994). Furthermore, if patients can be honest about their QoL concerns without the pressure of a face-to-face interview, self-administered assessments may be more valid than interview assessments. In any event, self-report data collection is cost-effective : research consistently shows that personal interviews cost 3-10 times as much as self-report paper-and-pencil approaches (Anderson et al, 1986).
Reliability and validity
Evidence is provided here for the reliability and validity of the SQLS, a
novel schizo-phrenia-specific QoL measure. Content validity has been addressed
by developing items on the basis of in-depth interviews, rather than relying
on the literature or clinical scales in this field. The content of the
questionnaire addresses experiences of importance to individuals with the
disorder. Items that were criticised by respondents as being meaningless or
ambiguous were removed. Internal consistency reliabilities of the three scale
domains incorporated in the measure have been shown to be high, and all items
in each scale correlate well with the overall scale score. Construct validity
was explored by correlation of the scales of the SQLS with established
psychiatric self-report measures and the SF-36. Results suggest that the
measure is addressing areas related, but not identical, to those of previously
existing measures.
We considered the appropriateness of other psychometric properties.
Criterion validity assumes a gold standard : we do not have one. The only
time one can really assess criterion validity is when a short form is compared
to its parent (longer) form : i.e. comparing SF-12 results with SF-36 results.
Concurrent validity assumes that two measures being compared are measuring the
same phenomenon : we are not in that situation - the SQLS is disease-specific
and does not measure, or claim to measure the same concepts as measured, for
example, by the SF-36. We did not attempt to measure aspects of predictive
validity, which would require separate studies. We consider that test-retest
is not necessary, as the statistic indicates that responses are
non-random and consequently reflective of an underlying phenomenon.
Clinical usefulness
The SQLS was developed to be a valid and feasible questionnaire for
self-completion that addresses the perceptions and concerns of people with
schizophrenia - except, of course, those too unwell to complete the
questionnaire. Its main use is likely to be in clinical trials and the
evaluation of clinical interventions. Evidence is presented in this report to
suggest that the SQLS has desirable properties in terms of reliability and
validity, and we have found the measure to have excellent acceptability and
feasibility in practice. The patients taking part in the development of the
instrument appeared to cover a broad range of intelligence, reading ability
and educational attainment, although these attributes were not tested.
The SQLS does not purport to assess all of patients' concerns and it is not intended to replace conventional outcome measures. However, it adds important information to that traditionally collected in psychiatry. Further work is under way to test its psychometric properties in different clinical contexts and in respondents with different levels of clinical severity. It is possible to be optimistic that the impact of schizophrenia on individuals' lives can now more directly be considered when treatments for the disease are evaluated.
![]() |
APPENDIX |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Copies of the SQLS and user's manual are available from Diane Wild, Oxford Outcomes, Bury Knowle Coach House, North Place, Old High Street, Headington, Oxford OX3 9HY ; e-mail : Oxford.outcomes@btinternet.com.
![]() |
CLINICAL IMPLICATIONS AND LIMITATIONS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LIMITATIONS
![]() |
ACKNOWLEDGMENTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Awad, A.G., Voruganti, L. N. P. & Heslegrave, R. J. (1997) Measuring quality of life in patients with schizophrenia. Pharmacoeconomics, 11, 32-47.[Medline]
Baker, F. & Intagliata, J. (1982) Quality of life in the evaluation of community support systems. Evaluation and Program Planning 5, 69 -79.[CrossRef][Medline]
Becker, M., Diamond, R. & Sainfort, F. (1993) A new patient focussed index for measuring quality of life in persons with severe and persistent mental illness. Quality of Life Research, 2, 239 -251.[Medline]
Bergner, M., Bobbitt, R. A., Carter, W. B., et al (1981) The Sickness Impact Profile : development and final revision of a health status measure. Medical Care, 19, 787 -805.[Medline]
Bigelow, D. A., Olson, M. M., Smoyer, S., et al (1991) Quality of Life Questionnaire : Respondent Self-report Version. I : Guidelines; II : Interview schedule. Portland, OR : Oregon Health Sciences University.
Boyle, G. J. (1991) Does item homogeneity indicate internal consistency or item redundancy in psychometric scales ? Personality and Individual Differences, 12, 291 -294.[CrossRef]
Cronbach, L. J. (1951) Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297 -334.
Goldberg, D.P. & Williams, P. (1988) A User's Guide to the General Health Questionnaire. Windsor : NFER-Nelson.
Greenley, J. R. & Greenberg, J. (1994) Measuring Quality of Life : A New and Practical Survey Instrument, Paper Series 38, Madison, WI : Mental Health Research Centre.
Hattie, J. (1985) Methodology review : assessing unidimensionality of tests and items. Applied Psychological Measurement, 9, 139 -163.
Heinisch, M., Ludwig, M. & Bullinger, M. (1991) Psychometrische Testung der Munchner Lebensqualitats Dimensionen Liste (MLDL). In Lebensqualitat bei Kardiavaskularen Erkrankungen (eds M. Bullinger, M. Ludwig & N. von Steinbuchel), pp. 73-90. Gottingen : Hogrefe.
Heinrichs, D. W., Hanlon, T. E. & Carpenter W.T. (1984) The quality of life scale : an instrument for rating the schizophrenic deficit syndrome. Schizophrenia Bulletin, 10, 388 -398.[Medline]
Hunt, S. M. & McKenna, S. P. (1993) Measuring quality of life in psychiatry. In Quality of Life Assessment : Key Issues in the 1990s (eds S. R. Walker & R. M. Rosser). London : kluwer.
Hunt, S. M. McEwen, J. & McKenna, S. (1986) Measuring Health Status. London : Croom Helm.
Nunally, J. C., Jr (1978) Introduction to Psychological Measurement. New York : McGraw-Hill.
Nunally, J. C., Jr & Bernstein, I. H. (1994) Psychometric Theory (3rd edn). New York : McGraw-Hill.
Oliver, J. P. J., Huxley, P. J., Bridges, K., et al (1996) Quality of Life and Mental Health Services. London : Routledge.
Orley, J., Saxena, S. & Herrman, H. (1998) Quality of life and mental illness. Reflections from the perspective of the WHOQOL. British Journal of Psychiatry, 172, 291 -293.[Medline]
Priebe, S., Roder-Waner, U. & Kaiser, W. (1999) Application and results of the Manchester Short Assessment of Quality of Life (MANSA). International Journal of Social Psychiatry, 45, 7 -12.[Medline]
Sartorius, N. (1997) Fighting schizophrenia and its stigma. A new World Psychiatric Association educational programme. British Journal of Psychiatry, 170, 297.[Medline]
Skantze, K., Malm, U., Dencker, S. J., et al (1992) Comparison of quality of life with standard of living in schizophrenia out-patients. British Journal of Psychiatry, 161, 797 -801.[Abstract]
Stein, L. I. & Test, M. A. (1980) Alternative to mental hospital treatment. I. Conceptual model, treatment program, and clinical evaluation. Archives of General Psychiatry, 37, 392 -397.[Abstract]
Ware, J. & Sherbourne, C. (1992) The MOS 36-item Short-Form Health Survey. I : Conceptual framework and item selection. Medical Care, 30, 473 -483.[Medline]
Ware, J., Kosinski, M. & Keller, S. D. (1994) SF-36 Physical and Mental Health Summary Scales : A User's Manual. Boston, MA : The Health Institute, New England Medical Centre.
Zigmond, A. & Snaith, R. (1983) The hospital anxiety and depression scale. Acta Psychiatrica Scandinavica, 67, 361 -370.[Medline]
Received for publication August 18, 1999. Revision received March 9, 2000. Accepted for publication March 24, 2000.