4817.0.55.001 - Information Paper: Use of the Kessler Psychological Distress Scale in ABS Health Surveys, Australia, 2001
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 21/05/2003
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1. BACKGROUND 1.1 The inclusion of Kessler Psychological Distress Scale - 10 (K10) in ABS Surveys 1. In 1997 the Australian Bureau of Statistics (ABS) conducted the National Survey of Mental Health and Wellbeing (SMHWB). The survey was an initiative of, and funded by, the then Commonwealth Department of Health and Family Services (HFS) as part of the National Mental Health Strategy. The primary purpose of the SMHWB was to provide information on the prevalence of a range of major mental disorders in Australian adults. The range of mental disorders included in this survey was determined by a Technical Advisory Committee, taking the following into consideration: disorders that were expected to affect more than one per cent of the population; the capacity of the Composite International Diagnostics Interview (CIDI) to diagnose selected mental disorders; and the limitations of a household survey in identifying relevant population groups. The survey also offered an opportunity to compare several short modules which gave measures of general mental health. To this purpose, a range of short modules, including the General Health Questionnaire (GHQ12) and the Kessler 10 (K10) Scale were included in the SMHWB. 2. The components of the instruments used in the SMHWB, including the versions of CIDI and K10 and associated scoring algorithms, were developed and provided to the ABS by the Clinical Unit for Anxiety and Depression (CRUfAD), School of Psychiatry, University of New South Wales under a contract with the then Commonwealth Department of Health and Family Services. The focus of the survey was on a CIDI diagnosis in the last 12 months prior to interview rather than on lifetime prevalence. The version of the K10 asked questions on current psychological distress during the last 4 weeks prior to interview. 3. The K10 was selected for use in the 2001 NHS on the basis of its performance in the SMHWB compared to other short general measures, particularly GHQ-12. 1.2 Usage of the K10 in Australia 4. The focus of the K10 is to measure psychological distress and it does not include any questions to identify psychosis, as this is difficult using a brief questionnaire. The K10 instrument may be appropriate to estimate the needs of the population for community mental health services, as people with psychosis generally do get depressed (Andrews & Slade, 2001). For these reasons, the K10 scale has been chosen for ABS health surveys, routine public health telephone surveys in a number of Australian states, and for use on patients in contact with mental health services in NSW. 5. As mentioned above, the usage of the K10 in Australia stemmed from its selection for use in the ABS 1997 SMHWB. The survey results enabled comparison of the K10 with other measures, including medical diagnosis (CIDI). A strong association was found between K10 scores and the diagnosis of anxiety and depression based on the CIDI. 6. The K10 has also been included in a number of State surveys including the New South Wales (NSW) Continuous Health Survey, the 2000 Health and Wellbeing Survey (conducted by the Health Department of Western Australia in collaboration with the South Australian and Northern Territory Health Departments and the then Commonwealth Department of Health and Aged Care), South Australian Health & Wellbeing Survey 2000 and the 2001 Victorian Population Health Survey. It was included in the 2001 National Health Survey (NHS) conducted by the ABS and administered to adults aged 18 years and over. The K10 was included in the 2001 NHS because it was found to be a better predictor of mental health and psychological distress compared with the other short general modules used in the 1997 SMHWB (see Appendix 1 for the question module). 1.3 Development of the K10 7. The K10 is a scale measuring non-specific psychological distress. It was developed in 1992 by Professors Ron Kessler and Dan Mroczek, as a short dimensional measure of non-specific psychological distress in the anxiety-depression spectrum, for use in the United States National Health Interview Survey (US-NHIS) (Kessler & Mroczek 1992, 1994). The scale consists of ten questions about non-specific psychological distress and seeks to measure the level of current anxiety and depressive symptoms a person may have experienced in the four weeks prior to interview. Other time periods can be used as a substitute for the last four weeks. For example, in the US the last month time period is used. 8. In developing the K10, Kessler and Mroczek reviewed approximately 500 initial items from various sources, reducing these to 45 items. In 1992, a mail survey was conducted in the US including 45 psychological distress items (n=1401). Using the data from this survey, Kessler and Mroczek refined their scale to 32 items. The following year, a telephone survey was conducted using the 32 items (n=1574). Based on the data from this survey Kessler and Mroczek were able to determine two sets of items. One set contained 6 items (named the K6) and the other contained 10 items (named the K10). These two sets of items represented the entire range of high distress and were discriminating along that continuum (Andrews & Slade 2001). 9. The K10 questionnaire yields a measure of psychological distress based on questions about negative emotional states experienced by respondents in the four weeks prior to interview. It contains low through to high threshold items. For each item there is a five-level response scale based on the amount of time the respondent reports experiencing the particular problem. The response options are: - none of the time; - a little of the time; - some of the time; - most of the time; and - all of the time. 10. Generally, each item is scored from 1 for 'none of the time' to 5 for 'all of the time'. Scores for the ten items are then summed, yielding a minimum possible score of 10 and a maximum possible score of 50, with low scores indicating low levels of psychological distress and high scores indicating high levels of psychological distress. Its important to note that the scoring algorithm used in the 1997 SMHWB has the reverse of this score so that low scores indicate high levels of psychological distress and high scores indicate low levels of psychological distress. Therefore the users of the 1997 SMHWB Confidentialised Unit Record File (CURF) need to recalculate scores to enable direct comparisons with the 2001 NHS CURF. 11. Currently there is no international or Australian standard method for the presentation of the K10 scores. 2 ALTERNATIVE MEASURES OF MENTAL HEALTH 12. Several other known measures of mental health can be used in population health surveys, including the CIDI and GHQ. Both were used in the face-to-face 1997 SMHWB. The CIDI instrument identifies potential symptoms of mental health problems and probes these symptoms to identify the level of severity (or clinical significance) and eliminates other causes such as drugs and illness. Specific combinations of appropriate symptoms may lead to the diagnosis of a particular mental disorder (for example depression). 2.1 Comparison between the K10 and other measures 14. Research has revealed a strong association between high scores on the K10 and a current CIDI diagnosis of anxiety and affective disorders. There is a lesser but significant association between the K10 and other mental disorder categories, or with the presence of any current mental disorder (Andrews & Slade, 2001). Sensitivity and specificity data analysis has indicated that the K10 is appropriate as a screening instrument to identify likely cases of anxiety and depression in the community (Korten, submitted). Recent research by Furukawa et al (2003) found that the K6 and K10 have better overall discriminatory power than the GHQ-12 in detecting DSM-IV depressive and anxiety disorders. Additional research has shown that the brevity, strong psychometric properties and ability to discriminate DSM-IV cases from non-cases makes the K6 and K10 attractive for use in general-purpose health surveys. Comparative analysis has shown that K6 and K10 outperform previously developed screening scales of comparable length in discriminating DSM cases and non cases (Kessler et al 2003). 3. SCORING THE K10 15. As stated previously, respondent scores on the K10 can range from a minimum of 10 to a maximum of 50, with low scores indicating low levels of psychological distress. The creators of the K10 have not developed or published details on scoring the scale. As such there is no agreed standard for determining cut off points for low, medium and high levels of psychological distress. Various interpretations of scoring used to date in Australia are outlined below. 3.1 K10 ranges to approximate levels of psychological distress 16. A set of cut-off scores for the K10 was developed by the Clinical Research Unit for Anxiety and Depression (CRUfAD), School of Psychiatry, University of New South Wales (NSW) to determine the prevalence of anxiety or depressive disorders. These cut-off scores are shown below. CRUfAD has found that 78% of the population have a low level of psychological distress and are unlikely to need professional assistance. A further 20% have a medium level and are encouraged to use self help information and techniques provided through CRUfAD. The 2% of the population with a high level are strongly encouraged to see a doctor.
3.2 Standardised K10 Scoring method 19. The Epidemiology and Surveillance Branch of the NSW Department of Health used an alternative scoring method for the K10 in the NSW 1997 and 1998 Health Surveys. In this method, each item is scored from 1 for 'none of the time' to 5 for 'all of the time' and the 10 items are summed to give scores ranging between 10 and 50. These scores are then converted to a t-score, by subtracting the mean of the score and dividing by the standard deviation of the score. The t-scores are then standardised with a mean of 50 and standard deviation of 10. The cut-off is determined by taking one standard deviation above the mean, (value of 60) to determine a high level of psychological distress.
3.3 Scoring method and use in international surveys 20. In May 2002 the first report including the K6 data from the United States National Health Interview Survey (US-NHIS) was released. The K6 results were presented in an item by item tabulation of the percentage of people responding 'all or most of the time' and 'some of the time' by various demographic characteristics (The National Centre for Health Statistics 2002). The item by item reporting style assumes that each question is not related to any other K6 question. 21. Some publications have used a combination of methods to report the K10 results. For example, the South Australian Health and Wellbeing Survey 2000 results were reported using the CRUfAD method, standardised scoring method and the individual questions method (CPSE 2000). 22. The K10 has been used in a series of epidemiological surveys coordinated by Professor Kessler and his colleagues known as the World Mental Health 2000 (WMH 2000) initiative, under the auspices of the World Health Organization. These surveys are similar in form to the 1997 SMHWB and comprise the CIDI and a series of other measures, including the K10. The total number of people involved in the surveys is approximately 200,000 and the countries in which it is being administered include Canada, the United States, Brazil, Colombia, Mexico, Peru, Belgium, France, Germany, Italy, the Netherlands, Spain, the Ukraine, Israel, South Africa, China, India, Indonesia, Japan and New Zealand. Although the data are not yet available, it is important to note that the K10 will have been cross-validated against diagnosis in a wide range of studies in many countries. Furthermore, it is expected that once the data become available a cut-off scoring method will be developed. 4. SNAPSHOT COMPARISON - THE 2001 NHS AND THE 2001 VICTORIAN POPULATION HEALTH SURVEY 23. The 2001 Victorian Population Health Survey was in the field around the same time as the 2001 National Health Survey (February to November 2001). The results from the two surveys showed similar breakdowns of K10 results. The prevalence of high and very high levels of psychological distress were marginally higher in the Victorian Population Survey. Level of Psychological Distress(a) using the Victoria Population Health Survey cut-offs.
(b) Age standardised percentages. 5. TIME SERIES COMPARISONS 24. The K10 has only been included in two ABS surveys, the 1997 SMHWB and the 2001 NHS. While the K10 module in the 2001 NHS is deliberately the same as that used in the 1997 SMHWB, there are important differences between aspects of each survey, such as sample design and coverage, survey methodology and content. These differences affect the use of data, the degree of data comparability and the interpretation of apparent changes in the prevalence of psychological distress from 1997 to 2001. 5.1 Comparison between results from the 1997 SMHWB and the 2001 NHS Very High Level of Psychological Distress(a): Australia, 1997 and 2001
* estimate has a relative standard error of between 25% and 50% and should be used with caution. ** estimate has a relative standard error greater than 50% and is considered too unreliable for general use. (a) As measured by the Kessler 10 Scale, from which a score of 10 to 50 is produced. (b) Age standardised percentages. 25. In comparison with results from the 1997 SMHWB, the 2001 NHS results showed that the adult prevalence of very high level of psychological distress in Australia increased for all age groups and both sexes except for males aged 65 to 74 years. The age-standardised proportion of adults reporting a very high level of psychological distress in 2001 (3.6%) was over 1 percentage point higher than in the 1997 SMHWB (2.2%). The age-standardised proportion of males reporting a very high level of psychological distress increased from 1.9% in 1997 to 2.7% in 2001. For females, the proportion almost doubled (from 2.4% in 1997 to 4.4% in 2001). The increase was greatest for people aged 18-24 and females aged 35 years and over. For details regarding all levels of psychological distress refer to Appendix 2. 26. As shown above, there is an observable increase in the prevalence of high and very high levels of psychological distress reported through the K10 from the 1997 SMHWB and the 2001 NHS. This increase may have resulted from a number of factors, and is most likely to have resulted from the combination of these factors. 27. Specific factors include: actual increased prevalence of psychological distress, changes in survey methodology, heightened awareness (for example, through media campaigns) of the symptoms of psychological distress and/or improved identification and treatment of associated conditions. The increase is not attributable to the ageing of the population, as age-standardised comparisons using K10 have been made. 29. Most of the 2001 NHS interviews were conducted before the September 2001 attacks in the United States. Psychologists commented on the impact these attacks would have on the psychological state of some people. For example, it was suggested that people who were already depressed may become even more depressed. Analysis of pre September 11 responses and the limited amount of post September 11 2001 data from the 2001 NHS showed no increase in the prevalence of the very high level of psychological distress. Therefore the increase between 1997 and 2001 prevalence is not attributable to emotional responses to the September 11th attacks. GLOSSARY Age standardisation Age standardisation is used in this publication to allow the comparison of populations with different age structures. A standard age comparison is used, in this case the age composition of the 2001 NHS benchmark population of Australia. The age standardisation estimate or proportion is that which would have prevailed at another point in time or other geographic area should the actual population have the standard age composition. Anxiety disorders A mood disturbance. Includes mania, hypomania, bipolar affective disorder, depression and dysthymia. Composite International Diagnostic Interview (CIDI) A comprehensive modular interview which can be used to assess current and lifetime prevalence of mental disorders through measurement of symptoms and their impact on day-to-day activities. Depression A state of gloom, despondency or sadness lasting at least two weeks. The person usually suffers from low mood, loss of interest and enjoyment and reduced energy. Their sleep, appetite and concentration may be affected. DSM-IV Diagnostic and statistical manual for mental disorders (fourth edition). The DSM-IV focuses on clinical, research and educational purposes, supported by an extensive empirical foundation. General Health Questionnaire (GHQ-12) A general measure of mental health and wellbeing which was designed to detect psychiatric disorders among respondents in community settings. It does not provide a clinical diagnosis. Kessler 10 (K10) See psychological distress. Mental disorder According to the ICD-10 (International Classification of Disease - 10th revision) classification of mental and behavioural disorders, a disorder implies 'the existence of a clinically recognisable set of symptoms or behaviour associated in most cases with distress and with interference with personal function' (WHO 1992, p 5). Most diagnoses require criteria relating to severity and duration to be met. Mental health problem Problems with mental health, such as worry or sadness, regardless of whether or not they met criteria for mental disorders. Prevalence The number of cases of a disease present in a population at a given time. Psychological distress Derived from the Kessler Psychological Distress Scale-10 items (K10). This is a scale of non-specific psychological distress based on 10 questions about negative emotional states in the reference period (4 weeks) prior to interview. The K10 is generally scored from 10 to 50, with higher scores indicating higher level of distress; low scores indicate a low level of distress. Psychosis A mental disorder in which the person has strange ideas or experiences which are unaffected by rational argument and are out of keeping with the views of any cultural group that the person belongs to. Technical advisory committee For the 1997 SMHWB the technical advisory committee comprised Professor Scott Henderson (chair), Professor Gavin Andrews, Professor Wayne Hall, Professor Helen Herrman, Professor Assen Jablensky and Professor Robert Kosky. BIBLIOGRAPHY ABS Publications Mental Health and Wellbeing: Profile of Adults, Australia 1997 (cat. no. 4326.0) - published and unpublished data. 2001 National Health Survey: Summary of Results, Australia (cat. no. 4364.0) - published and unpublished data. Other Publications Andrews, G., Slade, T.(2001). Interpreting scores on the Kessler psychological distress scale (K10), Australian and New Zealand Journal of Public Health, Vol 25(6) Centre for Population Studies in Epidemiology, Department of Human Services South Australia.(2000). South Australian Health and Wellbeing Survey December 2000. Furukawa, T.A., Kessler, R.C., Slade, T., et al. (2003). The performance of the K6 and K10 screening scales for psychological distress in Australian National Survey of Mental Health and Well-Being, Psychological Medicine, 33, 357-362. Health and Wellbeing Survey 2000: Psychological distress in the Western Australian population. Health Department of Western Australia, June 2001. Kessler, R., Mroczek, D. Final Version of our Non-specific Psychological Distress Scale [memo dated 10/3/94]. Ann Arbort (MI): Survey Research Center of the Institute for Social Research. University of Michigan, 1994. Kessler, R.C., Andrews, G., Colpe, L., et al. (2002). Short Screening Scales to Monitor Population Prevalence and Trends in Non-specific Psychological Distress, Psychological Medicine, 32, 959-976. Kessler, R.C., Barker, P.R., Colpe, L.J., et al.(2003). Screening for serious mental illness in the general population, Arch Gen Psychiatry, Vol 60. Korten, A.(submitted). Screening for anxiety and depression in the Australian Population, Australian and New Zealand Journal of Public Health. The (US) National Center for Health Statistics (NCHS). (2002). Summary Health Statistics for U.S. Adults: National Health Interview Survey 1997, May 2002, Series 10, Number 205. Victorian Population Health Survey 2001: selected findings, State of Victoria, Department of Human Services, 2002. World Health Organization.(1992). The ICD-10 Classification of Mental and Behavioural Disorders Criteria for Research, World Health Organization, Geneva. Internet Sites Clinical Research Unit for Anxiety and Depression, http://www.crufad.unsw.edu.au WMH 2000 Survey, http://www.hcp.med.harvard.edu/icpe/WMH2000.html APPENDIX 1 K10 Question Module as used in the 1997 SMHWB & 2001 NHS The following questions are about your feelings in the past 4 weeks. 1. In the past 4 weeks, about how often did you feel tired out for no good reason? 2. (In the past 4 weeks,) about how often did you feel nervous? 3. (In the past 4 weeks,) about how often did you feel so nervous that nothing could calm you down? 4. (In the past 4 weeks,) about how often did you feel hopeless? 5. (In the past 4 weeks,) about how often did you feel restless or fidgety? 6. (In the past 4 weeks,) about how often did you feel so restless you could not sit still? 7. (In the past 4 weeks,) about how often did you feel depressed? 8. (In the past 4 weeks,) about how often did you feel that everything was an effort? 9. (In the past 4 weeks,) about how often did you feel so sad that nothing could cheer you up? 10. (In the past 4 weeks,) about how often did you feel worthless? Answer Scale All of the time Most of the time Some of the time A little of the time None of the time APPENDIX 2 Level of Psychological Distress(a): Australia, 1997 and 2001
** estimate has a relative standard error greater than 50% and is considered too unreliable for general use. (a) As measured by the Kessler 10 Scale, from which a score of 10 to 50 is produced. (b) Age standardised percentages. Document Selection These documents will be presented in a new window.
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