Background to current MM checklist

As Diederichs, Berger and Bartels10 highlight, there is no ‘gold standard’ measure of MM. Several measures of MM exist and have been developed for a variety of reasons, including different definitions of MM, different purposes for measuring MM, different required or available resources for data collection and the type of data available.7 ,21 Moreover, there are no definitive criteria for the selection of chronic conditions that qualify for MM and, therefore, no standardised list of the number and type of diseases to be included in a MM measure.10 In a review of the literature, de Groot, Beckerman, Lankhorst and Bauter22 found that there were 13 common measures of MM: 12 of these were disease indexes and one was a disease count.

Researchers who are interested in tallying the number of conditions that occur in patients as an outcome, or those examining the prevalence of MM, primarily use disease counts (eg, Bayliss et al21). To develop a disease count measure, researchers typically select and include the most common conditions found in the targeted population. For example, Bayliss et al21 reviewed the literature and selected the 25 most common chronic conditions for a US sample to include in their measure. They developed a subjective scale or disease count, where participants marked which diseases they had and then rated them in terms of severity (ie, how much each one affected their daily functioning).

Although different viewpoints exist regarding what conditions to include and how they should be selected for an MM disease count measure, guidelines21 ,23 have been proposed to address these issues, which are based on work yielded from systematic reviews in the area.

Guidelines for developing an MM checklist

Fortin et al23 proposed an operational definition of MM, whereby two or more diseases should be present in an individual and meet the diagnostic criteria for two separate areas of the Cumulative Illness Rating Scale (CIRS).24 The CIRS is a measure that weights the severity of MM. It is divided into sections based on 14 different organ systems. These organ systems are as follows: (1) Cardiac, (2) Vascular, (3) Haematopoietic, (4) Respiratory, (5) Eyes, Ears, Nose, Throat and Larynx, (6) Upper gastrointestinal (GI), (7) Lower GI, (8) Hepatic, (9) Renal, (10) Genitourinary, (11) Musculoskeletal, (12) Neurological, (13) Endocrine/Metabolic and Breast, and (14) Psychiatric. For a person to be considered to have a diagnosis of MM, chronic disease must be present in at least two different sections or organ systems. However, it is not necessary for a disease count to list either all conditions or all CIRS body systems. Fortin et al25 recommend a minimum of seven conditions and argued that any list of conditions included in a MM prevalence study should reflect the most common conditions in the population to be studied.

Process for developing the current MM checklist

In line with Fortin et al's26 recommendations, the conditions included in the current disease count questionnaire were obtained from two large-scale national reports on the Irish population more widely25 ,26 and four Irish research studies that had investigated the prevalence of MM and had compiled lists of conditions to examine.6 ,19 ,26 ,27 To ensure that the list of conditions met international best practice recommendations,21 ,23 in terms of which conditions to include in an MM disease count list, we then combined our study with one international study that examined MM in people living with CP.5 We also examined two of the most recent systematic reviews, which outline the most common conditions included in MM studies and contain recommendations for the type of conditions to be included in MM checklists.10 ,28 Following this, two healthcare practitioners were consulted and provided feedback on which conditions to include, and one clinician, who is an expert in chronic pain, reviewed the entire MM checklist. From this review process, the three additional categories of conditions included were as follows: renal disorders, hepatic disorders and headache disorders. Subsequently, we collapsed the conditions from this developmental process with respect to the CIRS organ system domains and removed any duplicate conditions, leaving us a total of 34 conditions across 10 organ domains (see table 1). We also added category options (eg, ‘Other cardiac conditions’) to ensure that useful data could be collected on conditions that did not appear on the list, as well as a final ‘Any other condition not listed’ category.

Structure of MM checklist and operational definition of MM

Based on Fortin et al's8 suggestion, a condition will be deemed suitable for inclusion as a MM when it meets one or both of the following criteria; a formal diagnosis has been provided by a doctor, and/or a person is receiving prescribed medication for the particular condition. To ensure that participants understand what each condition is, a lay definition derived from a medical definition for each condition (see US National Library of Medicine MeSH database29) will be provided (see online supplementary appendix A). Furthermore, similar to Bayliss et al,21 who created a subjective survey disease count measure of MM, the current measure will include a rating scale (from 1 to 5; 1 being least impactful and 5 being most impactful) measuring the impact that each condition has on their daily functioning. The inclusion of this rating scale will enable the research to identify which chronic conditions have more of an impact on daily functioning and, indeed, which disease combinations have more of a cumulative impact on daily functioning.

Health-related quality of life

The Medical Outcomes Short Form-12 (SF-12)30 will be used to assess health-related quality of life. The SF-12 is a general measure of health-related quality of life that has been used and validated with European populations.31 It gathers information across 8 health domains: general health, physical functioning, emotional role limitation, physical role limitation, mental health, bodily pain, vitality and social functioning. According to the norm-based method recommended by the test author, these items are scored to produce a mental component summary and physical component summary of health-related quality of life.30 Lower scores on either of these scales are indicative of a lower quality of life. Irish population norms are available32 and will be used for comparison with the present sample. The SF-12 has been used as a measure of health-related quality of life previously within CP research and MM research.20 ,33 ,34

Depression and anxiety

Depression will be measured using the Patient Health Questionnaire-9 item (PHQ-9). The PHQ-9 is a widely used and well validated measure of depression13 and it has been used with people living with chronic conditions.35 It contains 9 items that relate to the Diagnostic and Statistical Manual Fourth Edition (DSM IV) criteria for depression. The items are scored on a four-point Likert scale ranging from 0 ‘not at all’ to 3 ‘nearly every day’. The higher the score on the PHQ-9, the more symptom criteria a person meets. A cut-off score of above 10 indicates moderate depression and a score of above 15 indicates a clinical ‘case’ of moderately severe depression.

Anxiety will be measured using the generalised anxiety disorder 7-item (GAD-7). The GAD-7 is a validated and standardised measure of anxiety36 and has been recommended for use in CP studies.37 It is a 7-item questionnaire that presents items relating to how often over the past couple of weeks a person has felt bothered by each of the DSM IV symptom criteria for GAD. Items are scored on a four-point Likert scale ranging from 0 ‘not at all’ to 3 ‘nearly every day’. A higher overall score represents greater symptom severity.

Pain severity and disability

Pain-related severity and disability will be measured by the Chronic Pain Grade Questionnaire,38 commonly used in pain research. The Chronic Pain Grade Questionnaire categorises pain severity into one of four grades based on two dimensions: intensity and disability, depending on pain experiences in the previous 3–6 months. It contains seven items which can be completed by self-report, and includes questions both about the pain itself and its impact on daily functioning.

Pain intensity and interference

Intensity of pain and the degree of interference in the participant's life will be measured by the Brief Pain Inventory, specifically the short form of the tool.39 This includes nine items, to be completed by self-report, and asks about pain both now and over time. Two scores are given: pain severity (out of 40) and pain interference (out of 70). Higher scores indicate greater pain severity and interference.

Multimorbidity Illness Perceptions Scale

The Multimorbidity Illness Perceptions Scale (MULTIPleS)40 was developed to measure patient illness perceptions in the presence of MM. The MULTIPleS is a 22-item questionnaire. Each item has a Likert scale that runs from 0 to 3, where ‘0’ indicates that a person ‘strongly disagrees’ with an item and ‘3’ indicates that a person ‘strongly agrees’ with an item. Overall, the 22 items comprise five subscales: emotional representation, treatment burden, prioritising conditions, causal links and activity limitations. The MULTIPleS is a relatively new scale, so it has not yet been used as a measure in clinical research. However, Gibbons et al40 found that the scale provided a good fit to the Rasch model and demonstrated evidence of reliability and validity for each of the subscales.