Respiratory Medicine (1991) 85 (Supplement B), 13-16
The Living with Asthma Questionnaire M. E. HYLAND
Department of Psychology, Polytechnic South West, Plymouth, Devon PL4 8AA, U.K.
The 'Living with Asthma Questionnaire' is an asthma-specific quality of life scale for assessing patients' own subjective experiences of asthma. The purpose of the questionnaire is to assist individual patient management and to provide an outcome measure for use in clinical trials. The scale has 68 items and covers 11 domains of asthma experience which were derived from focus group discussions amongst asthma sufferers. The initial item set was refined through standard psychometric techniques using a total of 783 patients and there is no statistical evidence for independent, domain-specific subscales. Validation studies are described.
Introduction Health-related quality of life is a fashionable concept in modern medicine, but its current popularity often obscures two important facts. The first is that the methodology of quality of life assessment is quite varied: there are several different types of assessment method. Second, quality of life assessment can be used for different kinds of decision making in medicine. In this paper I examine the methodology underlying the 'Living with Asthma Questionnaire' in terms of its intended use. Quality of life is a measure of health which, along with measures of morbidity and mortality, can be used for medical decision making. Quality of life assessment can be a component in three different kinds of decision-making processes, each of which occurs at a different level of medical organization. At the level of the individual patient, quality of life assessment can be used to inform clinical decision making for particular patients. For example, if an asthmatic patient presents with reasonably good pulmonary function but reports sleepless nights, then the patient's physician may alter treatment to overcome the patient's sleep problems, a problem of health rather than morbidity. Similarly, a physician treating a sportsman or woman may alter treatment in accordance to the quality of life requirements of this group compared to a non-sporting group. A quality of life questionnaire provides a more formal way of making a health assessment, an assessment which otherwise must be made on the basis of conversation with the patient. At the level of particular diseases, quality of life assessment can be used to compare between different types of treatment. A well known instance where quality of life assessment is used in this way is in the 0954-611 I/91/0B0013 + 04 $03.00/0
comparison of treatments for hypertension. As several types of pharmaceutical treatment for hypertension have rather similar effects on morbidity, i.e. blood pressure, the treatments can also be compared, and hence selected for, in terms of the extent to which they disrupt quality of life. Thus, the quality of life benefits of treatments can be compared with their effects on morbidity and mortality in order to provide recommendations of one type of treatment over another. The current practice of including quality of life assessment in clinical trials is motivated largely by a desire to show the benefits of a particular novel treatment, when the improvement in morbidity may be small. Finally, at the level of groups of diseases, quality of life assessment can be used to assist decisions on the allocation of resources between therapies for different diseases. A description and defence of this economic use of quality of life assessment is provided b y Alan Williams in this supplement. Each of these different uses of quality of life assessment requires a scale with different kinds of properties. A major requirement of a scale used for economic purposes is that the scale should be a ratio or equal interval scale as it is necessary to show the quantitative changes in quality of life following treatment. This requirement for quantification is desirable but not necessary for the other two purposes where decisions can be made on ordinal comparisons between responses. A scale which is designed to inform clinical decisions on individual patients should be as broad as possible so as to include all possible kinds of quality of life deficit associated with that particular disease. Compared with a narrowlyfocussed scale, a broad scale produces a more inclusive picture of the patient's experience; but such broad scales can have the disadvantage of being quite lengthy. © 1991 Bailli6re Tindall
14
M. E. Hyland
If a scale is to be used in clinical trials to compare between two different treatments, then it is desirable, in the first instance, for the scale to be broad so that all possible benefits of the new treatment can be detected. In the long term, however, the scale may be restricted to those types of items which typically show improvement in clinical trials. Thus, after investigation a scale used in clinical trials may be shortened to those items which are best able to discriminate between treatment conditions. Of course, such shortening carries the risk that new treatments may improve quality of life in ways which were not possible before. The Living with Asthma Questionnaire is designed to be a broadly-focussed type of quality of life assessment suitable to assist decision making both for individual patients and for comparisons between treatments in clinical trials, With respect to use in clinical trials, the scale includes all types of items, not necessarily those which are likely to be sensitive to a particular treatment; there may be some value in the long term in shortening the scale to a clinical trial-specific version.
non-medical context, e.g. an hotel, and encouraged to discuss amongst themselves how asthma affected their lives. Such discussion amongst patients provides, with minimal prompting from a researcher, a variety of concerns relevant to asthma. At this stage, the representativeness of these concerns is unknown because the groups are small and not representative. Six focus groups were held, and comments by patients were classified into 11 categories or domains of experience affected by their asthma. These domains were: social/leisure, sport, holidays, work and other activities, sleep, colds, mobility, medication usage, effects on others, doctors, dysphoric states and attitudes. Items were constructed on the basis of patients' comments. The domain of sex was not mentioned in any of the focus groups. However, as the social constraint o f talking to strangers, some of whom were of the opposite sex makes such comment unlikely, it was decided to include some items referring to the effect of asthma on sexual behaviour and relationships. The first version of the questionnaire, AQ 1, was constructed with 101 items covering 12 domains of experience relevant to asthma.
Exclusivity and Inclusivity of Items in a Disease-specific Questionnaire
A Uni-dimensionai Versus a Multi-dimensional Scale
The Living with Asthma Questionnaire is designed to measure the patient's experiences of asthma and to be consistent with a recent definition t h a t ' "Quality of Life" represents the functional effect of an illness and its consequent therapy upon a patient, as perceived by the patient' (1). The questionnaire consists of items which have been selected on the basis of exclusivity and inclusivity. First, the items are exclusive to asthma. That is, in contrast to a general quality of life instrument, the patient is not asked about questions which are relevant to other diseases but irrelevant to asthma. Second, the questionnaire is designed to be inclusive of all aspects of life experience which commonly distinguish asthmatics from non-asthmatics. Although it is easy to establish that an item is irrelevant to asthma, the criterion of inclusivity is more difficult to achieve. When asked about their experiences of asthma, patients will respond in terms of their memory of past events, and memory can be affected by a variety of factors including the context where the question is asked (2). If physicians ask patients about their asthma in a clinic, there is always a risk that patients' recall will be affected by medical aspects of their situation and that they will forget to report on relevant factors which happen at home. To achieve inelusivity, the initial item set in the Living with Asthma Questionnaire was derived from focus groups where groups of patients were brought together in a
During the process of scale construction, it is necessary to decide whether: (a) the scale should be constructed with subscales which can be aggregated to gi~e an overall score; or (b) whether subscales should be avoided and only an overall score produced. There are two ways of making sucha decision. One is for the author of the scale to make a judgement, perhaps on the objectives of the scale or on any other aspect which seems relevant to that decision. The alternative is to use a psychometric procedure to establish, statistically, whether there are meaningful subscales or not. The most commonly used statistical procedure for doing this is called factor analysis (3), and it is a procedure which examines the intercorrelations between items in a questionnaire. In my particular case there were 12 domains of items. The method of factor analysis can help establish whether the intercorrelations between items within domains are higher than the intercorrelations between items in different domains. It is only if the intercorrelations within domains are substantially more than the intercorrelations between domains that the scale can be identified, psychometrically, as having more than one dimension. Factor analysis of data obtained from 101 patients who completed AQ1 established that the scale was not multi-dimensional (4). Instead, all items tended to correlate well with each other, and there was therefore no statistical reason for identifying subscales
Living with Asthma Questionnaire appropriate to different domains. The subsequent design of the scale was therefore based on the search for items which had good psychometric properties for a single dimensional scale.
Acquiesence Bias Although a majority ofcomments in the focus groups were negative, i.e. describing problems, there were some positive items, e.g. "Asthma makes no difference to my life'. Most quality of life scales consist only of negative items, and this introduces a potential bias into results. People respond to questionnaires with varying degrees of acquiesence bias, that is, the bias to say 'yes' to an item irrespective of its content. Ifa quality of life questionnaire is constructed with only negative items, then patients high in acquiesence will report a falsely low quality of life. It was therefore decided to introduce both positive and negative items into the Living with Asthma Questionnaire. The inclusion of both positive and negative items has the further advantage that inconsistent responses to positive and negative items in the same domain can be detected. Such inconsistencies may either be due to acquiesence bias, or simply because the patient has a poor questionnaire completion technique.
Item Refinement and Modification Many of the items in the original 101-item data set had psychometric properties which made them unsuited for inclusion in a uni-dimensional scale or which suggested changes to the wording of the item. Items which have a highly skewed response distribution (i.e. more than 70% of people responding in the same way to the item) and items with low factor loadings (i.e. less than 0.3) are conventionally excluded during the process of test construction so as to leave a final item set with consistent psychometric properties. The process of item refinement and modification is carried out through a series of gradually improving versions of the questionnaire. In the case of the Living with Asthma Questionnaire, AQI was modified to a 77-item version, AQ2. Data were obtained from 105 patients who completed AQ2 and, following a further factor analysis, a 72-item version, AQ3, was constructed. Four-hundred and five patients completed AQ3 and on the basis of psychometric analysis, four items were dropped to give a 68-item scale, AQ4, which was the final form of the Living with Asthma Questionnaire. The following modifications were carried out during the gradual refinement of the scale. First, the 'doctor' items were dropped after AQ2 as it was found that all
15
such items had low factor loadings. Second, a 'not applicable' response category was added as responses to an open-ended question at the end of the questionnaire indicated that patients wished to use this category rather than 'untrue of me' when an item referred to a difficulty which was irrelevant to their life style. Inconsistencies in the use of the "not applicable' category provides an additional method for evaluating the quality of questionnaire completion. Third, there was a systematic attempt to increase the number of positive items to produce a better counterbalanced scale. The positive items frequently had poor psychometric properties so that in the final version there are 24 positive items and 44 negative items.
Validity and Reliability Convergent validity of the scale is demonstrated by a high correlation, r = 0-66 (n = 76), with the Sickness Impact Profile. The most important form of validity for quality of life scales, however, is predictive validity. In one study (5), the Living with Asthma Questionnaire was given to patients attending an asthma clinic, but the results were not known to the physician at the time of prescription. Quality of life deficit as measured by the Living with Asthma Questionnaire correlated r=0-35 (n=40) with steroid prescribing, but steroid prescribing was unrelated to clinic assessed pulmonary function. These data suggest that the assessments made by the physicians when interviewing patients (at one particular clinic) provide an informal measure of quality of life similar to that obtained by the Living with Asthma Questionnaire, assessments which are then used for clinical decisions. Further predictive validity of the scale is demonstrated by its relationship to peak flow, r = - 0 - 4 4 (n =40), and its ability to discriminate between patients recruited through the asthma society and those recruited through GPs, the former having a poorer quality of life (4). The retest-reliability of the scale has been shown to be 0.9.
Conclusion The Living with Asthma Questionnaire is designed to be a screening device to assist individual patient management and as an outcome evaluation for use in clinical trials. The questionnaire is currently the most broadly based of the asthma-specific scales; it measures asthma-relevant experiences in 11 domains, and the items in different domains intercorrelate. The questionnaire can be self-completed or interviewerassisted. The latter technique is of value particularly for elderly patients, where the patient has poor reading skills or where the patient is unfamiliar with the task of
16
M. E. Hyland
completing questionnaires. However, the questionnaire is designed in such a way that it is possible to check for internal consistency and hence evaluate the quality of the patient's questionnaire completion skills. References 1. Schipper H, Clinch J, Powell V. Definitions and conceptual issues.In: Spiker B. ed. Quality of Life Assessments in Clinical Trials. New York: Raven Press, 1990.
2. Baddeley A. Human Memory: Theory and Practice. London: Erlbaum, 1990. 3. Gorsuch RL. Factor Analysis. Hillsdale, NJ: Erlbaum, 1983. 4. Hyland ME, Finnis S, Irvine SH. A scale for assessing quality of life in adult asthma st,fferers. J Psychosom Res 1991; 35: 99-I 10. 5. Hyland ME, Taylor M, Morice AH. Steroid prescribing for asthmatics: association with pulmonary function, Asthma Symptom Checklist, and Living with Asthma Questionnaire. Thorax. Submitted 1991,
The Living with Asthma Questionnaire M. E. HYLAND
Department of Psychology, Polytechnic South West, Plymouth, Devon PL4 8AA, U.K.
The 'Living with Asthma Questionnaire' is an asthma-specific quality of life scale for assessing patients' own subjective experiences of asthma. The purpose of the questionnaire is to assist individual patient management and to provide an outcome measure for use in clinical trials. The scale has 68 items and covers 11 domains of asthma experience which were derived from focus group discussions amongst asthma sufferers. The initial item set was refined through standard psychometric techniques using a total of 783 patients and there is no statistical evidence for independent, domain-specific subscales. Validation studies are described.
Introduction Health-related quality of life is a fashionable concept in modern medicine, but its current popularity often obscures two important facts. The first is that the methodology of quality of life assessment is quite varied: there are several different types of assessment method. Second, quality of life assessment can be used for different kinds of decision making in medicine. In this paper I examine the methodology underlying the 'Living with Asthma Questionnaire' in terms of its intended use. Quality of life is a measure of health which, along with measures of morbidity and mortality, can be used for medical decision making. Quality of life assessment can be a component in three different kinds of decision-making processes, each of which occurs at a different level of medical organization. At the level of the individual patient, quality of life assessment can be used to inform clinical decision making for particular patients. For example, if an asthmatic patient presents with reasonably good pulmonary function but reports sleepless nights, then the patient's physician may alter treatment to overcome the patient's sleep problems, a problem of health rather than morbidity. Similarly, a physician treating a sportsman or woman may alter treatment in accordance to the quality of life requirements of this group compared to a non-sporting group. A quality of life questionnaire provides a more formal way of making a health assessment, an assessment which otherwise must be made on the basis of conversation with the patient. At the level of particular diseases, quality of life assessment can be used to compare between different types of treatment. A well known instance where quality of life assessment is used in this way is in the 0954-611 I/91/0B0013 + 04 $03.00/0
comparison of treatments for hypertension. As several types of pharmaceutical treatment for hypertension have rather similar effects on morbidity, i.e. blood pressure, the treatments can also be compared, and hence selected for, in terms of the extent to which they disrupt quality of life. Thus, the quality of life benefits of treatments can be compared with their effects on morbidity and mortality in order to provide recommendations of one type of treatment over another. The current practice of including quality of life assessment in clinical trials is motivated largely by a desire to show the benefits of a particular novel treatment, when the improvement in morbidity may be small. Finally, at the level of groups of diseases, quality of life assessment can be used to assist decisions on the allocation of resources between therapies for different diseases. A description and defence of this economic use of quality of life assessment is provided b y Alan Williams in this supplement. Each of these different uses of quality of life assessment requires a scale with different kinds of properties. A major requirement of a scale used for economic purposes is that the scale should be a ratio or equal interval scale as it is necessary to show the quantitative changes in quality of life following treatment. This requirement for quantification is desirable but not necessary for the other two purposes where decisions can be made on ordinal comparisons between responses. A scale which is designed to inform clinical decisions on individual patients should be as broad as possible so as to include all possible kinds of quality of life deficit associated with that particular disease. Compared with a narrowlyfocussed scale, a broad scale produces a more inclusive picture of the patient's experience; but such broad scales can have the disadvantage of being quite lengthy. © 1991 Bailli6re Tindall
14
M. E. Hyland
If a scale is to be used in clinical trials to compare between two different treatments, then it is desirable, in the first instance, for the scale to be broad so that all possible benefits of the new treatment can be detected. In the long term, however, the scale may be restricted to those types of items which typically show improvement in clinical trials. Thus, after investigation a scale used in clinical trials may be shortened to those items which are best able to discriminate between treatment conditions. Of course, such shortening carries the risk that new treatments may improve quality of life in ways which were not possible before. The Living with Asthma Questionnaire is designed to be a broadly-focussed type of quality of life assessment suitable to assist decision making both for individual patients and for comparisons between treatments in clinical trials, With respect to use in clinical trials, the scale includes all types of items, not necessarily those which are likely to be sensitive to a particular treatment; there may be some value in the long term in shortening the scale to a clinical trial-specific version.
non-medical context, e.g. an hotel, and encouraged to discuss amongst themselves how asthma affected their lives. Such discussion amongst patients provides, with minimal prompting from a researcher, a variety of concerns relevant to asthma. At this stage, the representativeness of these concerns is unknown because the groups are small and not representative. Six focus groups were held, and comments by patients were classified into 11 categories or domains of experience affected by their asthma. These domains were: social/leisure, sport, holidays, work and other activities, sleep, colds, mobility, medication usage, effects on others, doctors, dysphoric states and attitudes. Items were constructed on the basis of patients' comments. The domain of sex was not mentioned in any of the focus groups. However, as the social constraint o f talking to strangers, some of whom were of the opposite sex makes such comment unlikely, it was decided to include some items referring to the effect of asthma on sexual behaviour and relationships. The first version of the questionnaire, AQ 1, was constructed with 101 items covering 12 domains of experience relevant to asthma.
Exclusivity and Inclusivity of Items in a Disease-specific Questionnaire
A Uni-dimensionai Versus a Multi-dimensional Scale
The Living with Asthma Questionnaire is designed to measure the patient's experiences of asthma and to be consistent with a recent definition t h a t ' "Quality of Life" represents the functional effect of an illness and its consequent therapy upon a patient, as perceived by the patient' (1). The questionnaire consists of items which have been selected on the basis of exclusivity and inclusivity. First, the items are exclusive to asthma. That is, in contrast to a general quality of life instrument, the patient is not asked about questions which are relevant to other diseases but irrelevant to asthma. Second, the questionnaire is designed to be inclusive of all aspects of life experience which commonly distinguish asthmatics from non-asthmatics. Although it is easy to establish that an item is irrelevant to asthma, the criterion of inclusivity is more difficult to achieve. When asked about their experiences of asthma, patients will respond in terms of their memory of past events, and memory can be affected by a variety of factors including the context where the question is asked (2). If physicians ask patients about their asthma in a clinic, there is always a risk that patients' recall will be affected by medical aspects of their situation and that they will forget to report on relevant factors which happen at home. To achieve inelusivity, the initial item set in the Living with Asthma Questionnaire was derived from focus groups where groups of patients were brought together in a
During the process of scale construction, it is necessary to decide whether: (a) the scale should be constructed with subscales which can be aggregated to gi~e an overall score; or (b) whether subscales should be avoided and only an overall score produced. There are two ways of making sucha decision. One is for the author of the scale to make a judgement, perhaps on the objectives of the scale or on any other aspect which seems relevant to that decision. The alternative is to use a psychometric procedure to establish, statistically, whether there are meaningful subscales or not. The most commonly used statistical procedure for doing this is called factor analysis (3), and it is a procedure which examines the intercorrelations between items in a questionnaire. In my particular case there were 12 domains of items. The method of factor analysis can help establish whether the intercorrelations between items within domains are higher than the intercorrelations between items in different domains. It is only if the intercorrelations within domains are substantially more than the intercorrelations between domains that the scale can be identified, psychometrically, as having more than one dimension. Factor analysis of data obtained from 101 patients who completed AQ1 established that the scale was not multi-dimensional (4). Instead, all items tended to correlate well with each other, and there was therefore no statistical reason for identifying subscales
Living with Asthma Questionnaire appropriate to different domains. The subsequent design of the scale was therefore based on the search for items which had good psychometric properties for a single dimensional scale.
Acquiesence Bias Although a majority ofcomments in the focus groups were negative, i.e. describing problems, there were some positive items, e.g. "Asthma makes no difference to my life'. Most quality of life scales consist only of negative items, and this introduces a potential bias into results. People respond to questionnaires with varying degrees of acquiesence bias, that is, the bias to say 'yes' to an item irrespective of its content. Ifa quality of life questionnaire is constructed with only negative items, then patients high in acquiesence will report a falsely low quality of life. It was therefore decided to introduce both positive and negative items into the Living with Asthma Questionnaire. The inclusion of both positive and negative items has the further advantage that inconsistent responses to positive and negative items in the same domain can be detected. Such inconsistencies may either be due to acquiesence bias, or simply because the patient has a poor questionnaire completion technique.
Item Refinement and Modification Many of the items in the original 101-item data set had psychometric properties which made them unsuited for inclusion in a uni-dimensional scale or which suggested changes to the wording of the item. Items which have a highly skewed response distribution (i.e. more than 70% of people responding in the same way to the item) and items with low factor loadings (i.e. less than 0.3) are conventionally excluded during the process of test construction so as to leave a final item set with consistent psychometric properties. The process of item refinement and modification is carried out through a series of gradually improving versions of the questionnaire. In the case of the Living with Asthma Questionnaire, AQI was modified to a 77-item version, AQ2. Data were obtained from 105 patients who completed AQ2 and, following a further factor analysis, a 72-item version, AQ3, was constructed. Four-hundred and five patients completed AQ3 and on the basis of psychometric analysis, four items were dropped to give a 68-item scale, AQ4, which was the final form of the Living with Asthma Questionnaire. The following modifications were carried out during the gradual refinement of the scale. First, the 'doctor' items were dropped after AQ2 as it was found that all
15
such items had low factor loadings. Second, a 'not applicable' response category was added as responses to an open-ended question at the end of the questionnaire indicated that patients wished to use this category rather than 'untrue of me' when an item referred to a difficulty which was irrelevant to their life style. Inconsistencies in the use of the "not applicable' category provides an additional method for evaluating the quality of questionnaire completion. Third, there was a systematic attempt to increase the number of positive items to produce a better counterbalanced scale. The positive items frequently had poor psychometric properties so that in the final version there are 24 positive items and 44 negative items.
Validity and Reliability Convergent validity of the scale is demonstrated by a high correlation, r = 0-66 (n = 76), with the Sickness Impact Profile. The most important form of validity for quality of life scales, however, is predictive validity. In one study (5), the Living with Asthma Questionnaire was given to patients attending an asthma clinic, but the results were not known to the physician at the time of prescription. Quality of life deficit as measured by the Living with Asthma Questionnaire correlated r=0-35 (n=40) with steroid prescribing, but steroid prescribing was unrelated to clinic assessed pulmonary function. These data suggest that the assessments made by the physicians when interviewing patients (at one particular clinic) provide an informal measure of quality of life similar to that obtained by the Living with Asthma Questionnaire, assessments which are then used for clinical decisions. Further predictive validity of the scale is demonstrated by its relationship to peak flow, r = - 0 - 4 4 (n =40), and its ability to discriminate between patients recruited through the asthma society and those recruited through GPs, the former having a poorer quality of life (4). The retest-reliability of the scale has been shown to be 0.9.
Conclusion The Living with Asthma Questionnaire is designed to be a screening device to assist individual patient management and as an outcome evaluation for use in clinical trials. The questionnaire is currently the most broadly based of the asthma-specific scales; it measures asthma-relevant experiences in 11 domains, and the items in different domains intercorrelate. The questionnaire can be self-completed or interviewerassisted. The latter technique is of value particularly for elderly patients, where the patient has poor reading skills or where the patient is unfamiliar with the task of
16
M. E. Hyland
completing questionnaires. However, the questionnaire is designed in such a way that it is possible to check for internal consistency and hence evaluate the quality of the patient's questionnaire completion skills. References 1. Schipper H, Clinch J, Powell V. Definitions and conceptual issues.In: Spiker B. ed. Quality of Life Assessments in Clinical Trials. New York: Raven Press, 1990.
2. Baddeley A. Human Memory: Theory and Practice. London: Erlbaum, 1990. 3. Gorsuch RL. Factor Analysis. Hillsdale, NJ: Erlbaum, 1983. 4. Hyland ME, Finnis S, Irvine SH. A scale for assessing quality of life in adult asthma st,fferers. J Psychosom Res 1991; 35: 99-I 10. 5. Hyland ME, Taylor M, Morice AH. Steroid prescribing for asthmatics: association with pulmonary function, Asthma Symptom Checklist, and Living with Asthma Questionnaire. Thorax. Submitted 1991,
