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'HRQL questionnaire' OSQOL

Battery: SOS Quality of Life Survey

Generic: SF-36 Scales

Generic: SF-36 Summary Scores

Generic: SF-36 Scales

Generic: SF-36 Scales

Specific: OSQOL

Generic: SF-36 Scales and Summary Scores Interview

Specific: Gastric Bypass Questionnaire

Battery: Gothenburg Quality of Life Scale and others

Generic: Nottingham Health Profile

Battery: Quality of Life Index and others Generic: SF-36 Scales Generic: Rosser Index Specific: Harris hip score questionnaire

Generic: SF-36 Kellner questionnaire

Battery: SOS Quality of Life Survey

Generic: Sickness Impact Profile (SIP), Mood Adjective Check List (MACL) Specific: Three-Factor Eating Questionnaire (TEFQ)

Generic: SF-36 and others found in the interpretation guidelines for the SF-36 Health Survey (35).

Since quality of life measurement scores have no direct commonly understood meaning, the clinical significance of different scale levels may be difficult to interpret for the inexperienced user. To be more user-friendly scores are sometimes transformed into a 0-to-100 scale, which facilitates the understanding of differences in scores and also enables scores of different measures within an instrument to be compared along a uniform scale (cf. SF-36 health profiles in Figures 33.2 and 33.3), A common way to evaluate the impact on quality of life is to relate patient scores to the scores of reference groups.

'Known group' comparisons may include norm-based interpretation linked to the analysis of score distributions in characterized clinical as well as general populations (cf. SIP category and index scores of severely obese vs. those of healthy subjects and cancer survivors in Figures 33.4 and 33.6, respectively). It is also useful to calculate the percentage of the study sample with no reported limitation on the different functional health scales, versus proportions with small-to-moderate and large dysfunction. Among other distribution-based interpretation methods to convey differences in quality of life scores, calculation of effect sizes should be mentioned. Effect size estimates allow direct comparisons across different measures regardless of scoring system and the clinical significance of differences between groups may be judged against standard criteria proposed by Cohen (46).

The clinical meaning of change in intervention studies is another important issue. To arrive at meaningful interpretations, quality of life change scores may be compared, or anchored to other established criteria for clinical change. Obviously, effects of obesity interventions on quality of life may be related to weight change and to reductions in morbidity. It should be noted, however, that initial weight loss or participation per se in weight management programmes is likely to produce unrealistic short-term changes, and repeated post-treatment assessments, including long-term follow-up of quality of life, are strongly recommended (19,47). The issue of clinically meaningful change could also be elucidated by calculating effect sizes of change (48). Standardized response means, SRM (49), is one of several methods used to estimate the responsiveness of measures in intervention studies (cf. SOS Quality of Life Survey change over time in Figure 33.8). Changes in score levels can also become meaningful by comparing them with 'normality' defined by population norms or with the impact of observed life events, such as being laid off from work.

Understanding individual scores sometimes requires thresholds indicating current or future morbidity, e.g. to estimate the prevalence of mood disorder in obese populations (cf. HAD scale and probabilities of depression in Figure 33.10). These well-established means of interpretation are all the more important in the field of obesity where the experience of quality of life measures is scanty.

HRQL and Obesity I: Obese Subjects vs. General Population Norms

The impact of obesity on quality of life has mainly been studied in clinical investigations where it is not known if samples are representative of the total obese population. It has been shown that obese subjects who seek treatment for their obesity report greater psychopathology than those who do not seek treatment (50). Both obese groups in that study, however, reported more distress than did normal weight controls. In the Swedish Obese Subjects (SOS) study, the severely obese who chose surgical treatment had generally lower levels of quality of life before treatment than their matched obese controls (19). Thus, it is crucial to perform population studies that include generic questionnaires in order to determine the extent and nature of the burden of obesity in relation to general population norms. Recently, three studies have used the SF-36 Health Survey to study the impact of obesity on quality of life in general population samples. The SF-36 is a widespread, generic short-form instrument, which comprises eight core domains of health-related quality of life: physical functioning, role functioning-physical, bodily pain, general health, vitality, social functioning, role functioning-emotional, and mental health (35,36,44).

Le Pen et al. (43) compared the SF-36 health profiles of subjects classified as non-obese (BMI < 27), overweight (BMI 27-30) or obese (BMI > 30) in a French community sample. The overweight group did not differ from the non-obese except for a slight but significant decrease in physical functioning. The obese group, however, showed impaired quality of life compared to the non-obese on five of eight SF-36 scales: physical functioning, role functioning-physical and bodily pain (scales which mainly reflect physical health aspects) and in general health and vitality (scales reflecting both physical and mental health aspects). Unexpectedly, no differences between groups were observed on the mental health scales (social functioning, role functioning-emotional, and mental health).

Han et al. (51) used the SF-36 to evaluate the impact of abdominal fat (large waist circumferences) as well as generalized obesity (high BMI) on quality of life in a Dutch population sample. The total sample was divided by sex and tertiles of waist circumference and BMI. Odds ratios were cal

Figure 33.2 SF-36 health profiles in relation to body mass index (BMI) in a Swedish population study. A higher score (range 0-100) on the SF-36 scales represents better health status. Subjects are grouped in five categories of BMI: underweight (BMI < 18.5), normal weight (18.5 < BMI < 25), overweight (25 < BMI < 30), obesity (30 < BMI < 40) and massive obesity (BMI > 40). Calculations of BMI are based on self-reported height and weight. PF, physical functioning; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social functioning; RE, role-emotional; MH, mental health

Figure 33.2 SF-36 health profiles in relation to body mass index (BMI) in a Swedish population study. A higher score (range 0-100) on the SF-36 scales represents better health status. Subjects are grouped in five categories of BMI: underweight (BMI < 18.5), normal weight (18.5 < BMI < 25), overweight (25 < BMI < 30), obesity (30 < BMI < 40) and massive obesity (BMI > 40). Calculations of BMI are based on self-reported height and weight. PF, physical functioning; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social functioning; RE, role-emotional; MH, mental health culated (adjusted for age, socioeconomic and lifestyle factors) for poor health status, defined as a scale score below 66.7 (score range 0-100). Men and women in the upper tertiles of waist circumference (mean 104.3 cm) as well as BMI (mean 29.6) were more likely to have poor physical functioning. Subjects with generalized obesity were more likely to report bodily pain and women also reported poorer general health perceptions. No adverse effects of abdominal fat or generalized obesity were observed on role functioning-physical, vitality, social functioning, role functioning-emotional, and mental health.

Brown et al. (52) presented SF-36 data from a large (n = 14431) population-based study of Australian women 45-49 years of age. Around half of the sample had a BMI > 25. The study corroborated earlier findings that the physical aspects of HRQL (physical functioning, bodily pain and general health) and vitality deteriorate with increasing BMI. Furthermore, even after adjusting for area of residence, education, smoking, exercise and meno-pausal status they found both high and low BMI to be associated with worse HRQL. The study pro vided additional support from the HRQL perspective for an optimal BMI range of 20-25.

We will use SF-36 data from two Swedish population studies to further illustrate this type of norm-based interpretation. In the first example, SF-36 health profiles from subjects with underweight and increasing degrees of overweight are compared with the normal weight persons in a 1997 population study in a Swedish county (Figure 33.2; Ulf Larsson et al., unpublished data). The total postal survey comprised a random sample of the adult population (n = 8751, 72% response rate). We used a sub-sample of subjects between 16 and 65 years of age to avoid confounding physical health with increasing age.

As shown in Figure 33.2 the pattern of impact is quite clear; the more overweight the worse the health profile and more so for physical aspects of health (physical functioning, role-physical, bodily pain and general health) than mental. There is a dramatic negative impact on all aspects of health when obesity is massive (BMI > 40). The difference, expressed in effect sizes, between the massively obese and normal weight subjects, was particularly

Figure 33.3 Comparison of SF-36 health profiles and summary scores between an obese (BMI > 30) population sample and age- and sex-matched Swedish population norms. Calculations of BMI are based on self-reported height and weight. A higher score on the SF-36 scales (range 0-100) and summary components represents better health status. The physical (PCS) and mental (MCS) component summary scores are weighted indexes (mean 50, SD 10) of the eight scales. The physically oriented scales (PF, RP, BP and GH) have the highest impact on PCS, while the mentally oriented scales (MH, RE, SF and VT) have the highest impact on MCS. A score of 50 on PCS and MCS represents the mean of the general Swedish population. PF, physical functioning; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social functioning; RE, role-emotional; MH, mental health; PCS, physical component summary score; MCS, mental component summary score. Differences between groups were tested by Fisher's non-parametric permutation test: *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001

Figure 33.3 Comparison of SF-36 health profiles and summary scores between an obese (BMI > 30) population sample and age- and sex-matched Swedish population norms. Calculations of BMI are based on self-reported height and weight. A higher score on the SF-36 scales (range 0-100) and summary components represents better health status. The physical (PCS) and mental (MCS) component summary scores are weighted indexes (mean 50, SD 10) of the eight scales. The physically oriented scales (PF, RP, BP and GH) have the highest impact on PCS, while the mentally oriented scales (MH, RE, SF and VT) have the highest impact on MCS. A score of 50 on PCS and MCS represents the mean of the general Swedish population. PF, physical functioning; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social functioning; RE, role-emotional; MH, mental health; PCS, physical component summary score; MCS, mental component summary score. Differences between groups were tested by Fisher's non-parametric permutation test: *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001

large on physical functioning and general health, and moderate on social functioning, bodily pain, vitality and mental health (data not shown). A lower health profile compared with the normal weight group can also be seen in the physical areas for obese persons (BMI 30-39.9) and for those with overweight (BMI 25-29.9). Vitality and social functioning are affected in the obese group (BMI 30-39.9) but, unexpectedly, not mental health. It is also notable that underweight persons (BMI < 18.5) report worse mental health in all aspects compared with the obese and overweight groups and worse physical health than the normal weight group.

Mental health scores among the normal weight, overweight and obese in the French, Dutch, Australian and Swedish population samples were unexpectedly similar. This finding indicates that the prevalence of mood disorders in a random population sample of overweight and obese persons does not, unlike the massively obese (BMI > 40.0), differ from that of the general population. However, the sensitivity of the mental health scale of the SF-36 to detect mental disturbances in overweight and obese samples should be further investigated.

In Figure 33.3, an obese population group (BMI > 30) is compared with a perfect age- and sex-matched Swedish SF-36 norm population (53), i.e. reference values representing the general population. The accuracy of comparisons with norm values requires that known systematic differences in self-rated health by demographics be taken into consideration. For example, physical health in particular decreases with age and women show generally lower health profiles than men. Thus, the advantage of a perfectly matched reference group is obvious. As shown in Figure 33.3, the health profile of the obese is clearly worse in all respects than the population norm. The SF-36 physical and mental summary scores are displayed to further emphasize the large differences between groups. It should be noted though that the health profile of the obese sample in Figure 33.3 is worse than that of the corresponding group (BMI 30-39) in Figure 33.2. The reasons for this are probably related to sample differences and thus more research is needed to clarify the impact of obesity on quality of life in general population samples.

There is no 'gold standard' quality of life instrument by which to assess the burden of obesity. On the contrary, since obesity is associated with a wide range of chronic conditions it would most likely be advantageous to compare results from different generic instruments. In the next example, the Sickness Impact Profile (SIP) is used to assess functional health in a sample of severely obese subjects. The SIP is a well-established self-report measure of health-related limitations in 12 defined areas of everyday life: body care and movement, mobility, ambulation, sleep and rest, eating, home management, work, recreation and pastimes, social interaction, communication, alertness behaviour and emotional behaviour. A physical, psychosocial, and overall index is also calculated.

In Figure 33.4, SIP dimension and index scores in a group of severely obese subjects from the SOS methods study (27) are compared with healthy reference subjects (39). The main features of the SOS registry and intervention studies can be seen in Figure 33.5.

The severely obese report more functional limitations in nearly all aspects of everyday life. Mobility-oriented areas are the most affected (body care and movement, mobility, and ambulation) together with home management, recreation and pastimes, and social interaction, all of which contain statements refering to mobility. SIP physical, psychosocial, and overall indexes show small to moderate effect sizes, i.e. the obese suffer from a wide variety of negative consequences in their ordinary lives compared with people in general. Also, more emotional behaviour dysfunction is reported by the obese. Behaviours not limited by obesity are: communication (primarily speech pathology), eating (mainly insufficient nutrition), and alertness behaviour (cognitive functioning). As shown in Figure 33.4b, effect size calculations are informative about both level and strength of the burden perceived by an obese sample compared with a reference group.

A disadvantage of the SIP is that eating problems of significance to obese people are not covered by the eating category. Rather SIP items comprise problems associated with poor nutrition due to lack of appetite, impairment, dexterity difficulties, etc. As an alternative to the SIP eating category, the Three-Factor Eating Questionnaire (TFEQ, Figure 33.1) is an appropriate and comprehensive measure of eating behaviour related to overweight and obese subjects (19,54-56).

Summary: How Obese Persons Differ From the General Population

• Poorer functioning and well-being, more in physical than mental aspects

• The more overweight, the worse HRQL

• Both physical and mental aspects affected in the massively obese

• Poorer HRQL in massive obesity than in underweight

HRQL and Obesity II: Obese Subjects Seeking Treatment vs. Other Groups of Chronically Ill and Disabled

In a US study, Fontaine et al. (57,58) used the SF-36 to assess quality of life in a consecutive sample of obese subjects seeking outpatient treatment. The obese scored significantly worse on all of the eight SF-36 scales compared with general US population norms. The largest differences were noted for the bodily pain and vitality scales. Further comparisons with reference values for other chronic medical conditions indicated that the impact of pain among obese subjects seeking treatment is considerable, equivalent to that of chronic migraine patients. This finding is of clinical importance and the effect of weight loss on chronic pain should be investigated.

In the next example, SIP category and index scores of the severely obese are compared with cancer survivors. As can be seen in Figure 33.6a, functional limitations in everyday life are in most areas worse in the severely obese than in an unselected group of cancer survivors 2-3 years after diagnosis (59). The differences are significant for several of the SIP categories and for all three summary indexes: physical, psychosocial, and overall. Restrictions are as common among the obese as in cancer survivors in areas representing mobility, sleep and rest, home

Figure 33.4(a) Mean scores of SIP categories and indexes for severely obese subjects (SOS) vs. reference subjects from the general population. High scores on SIP categories and indexes represent dysfunction.

BCM, body care and movement; M, mobility; A, ambulation; SR, sleep and rest; E, eating; HM, home management; W, work; RP, recreation and pastimes; SI, social interaction; C, communication; AB, alertness behaviour; EB, emotional behaviour; PH, physical index (mean of BCM, M and A); PS, psychosocial index (mean of SI, C, AB and EB); Overall, total SIP index (mean of all 12 categories). Differences between groups were tested by Fisher's non-parametric permutation test. ****P < 0.0001, ***p < 0.001, **P < 0.01, *P < 0.05, NS, not significant.

(b) Effect sizes of SIP categories and indexes for severely obese subjects (SOS) vs. reference subjects from the general population. Effect size was calculated as the mean scale score difference between groups divided by the pooled standard deviation

Figure 33.4(a) Mean scores of SIP categories and indexes for severely obese subjects (SOS) vs. reference subjects from the general population. High scores on SIP categories and indexes represent dysfunction.

BCM, body care and movement; M, mobility; A, ambulation; SR, sleep and rest; E, eating; HM, home management; W, work; RP, recreation and pastimes; SI, social interaction; C, communication; AB, alertness behaviour; EB, emotional behaviour; PH, physical index (mean of BCM, M and A); PS, psychosocial index (mean of SI, C, AB and EB); Overall, total SIP index (mean of all 12 categories). Differences between groups were tested by Fisher's non-parametric permutation test. ****P < 0.0001, ***p < 0.001, **P < 0.01, *P < 0.05, NS, not significant.

(b) Effect sizes of SIP categories and indexes for severely obese subjects (SOS) vs. reference subjects from the general population. Effect size was calculated as the mean scale score difference between groups divided by the pooled standard deviation

Figure 33.5 The Swedish Obese Subjects (SOS) study

The SOS study is an ongoing nationwide, multicentre project which comprises a registry study and an intervention trial. Since its start in October 1987 about 7000 severely obese persons have been accepted in the registry study. Inclusion criteria are age at accrual (37—57 years) and BMI > 34kg/m2 for males and BMI > 38 kg/m2 for females.

The intervention study is a controlled clinical trial designed to test if the negative effects of severe obesity on mortality, morbidity and quality of life are reduced during long-term weight reduction. The outcomes of surgical vs. conventional weight reduction treatment will include 2000 surgical cases and their matched controls followed for 10 years.

Health-related quality of life, HRQL. A battery of study-specific and generic questionnaires was designed to assess quality of life in the SOS study (see Appendix). Well-established HRQL measures, assumed to cover a broad range of health impacts of obesity, were supplemented by condition-specific parts, all suitable for large-scale mailout—mailback data collection.

management, work, and communication. Effect size calculations (Figure 33.6b) further illustrate the relative strength of functional impacts in the obese versus cancer survivors. The recreation and pastimes and social interaction domains are most negatively affected by obesity, although effect sizes are small to moderate (interval 0.20-0.50). Additional comparisons showed that the impact of obesity was equal to that of a subgroup of cancer survivors with one or more known recurrences. Only limitations in mobility were significantly worse in the recurrence group (data not shown).

In contrast, the level of impact of obesity on functional health is modest compared with disabling conditions such as rheumatoid arthritis or chronic pain syndrome, where limitations according to SIP overall index are three to four times greater (60). However, the severely obese report worse men tal well-being (Mood Adjective Check List; see Appendix) than a number of chronically ill or injured patient populations such as rheumatoid arthritis sufferers, cancer survivors with no recurrence 2—3 years after diagnosis, and people with spinal cord injuries several years after injury (39). The well-being of obese persons matches that of cancer survivors with recurrence and people with spinal cord injuries less than 2 years after injury. Only non-responders to treatment among patients with chronic pain syndrome score lower. Moreover, the severely obese report more symptoms of anxiety and depression (Hospital Anxiety and Depression scale; see Appendix) compared with spinal cord injured and disease groups such as generalized malignant melanoma and intermittent claudication.

Figure 33.6(a) Mean scores of SIP categories and indexes for severely obese subjects (SOS) vs. unselected cancer survivors. High scores on SIP categories and indexes represent dysfunction. BCM, body care and movement; M, mobility; A, ambulation; SR, sleep and rest; E, eating; HM, home management; W, work; RP, recreation and pastimes; SI, social interaction; C, communication; AB, alertness behaviour; EB, emotional behaviour; PH, physical index (mean of BCM, M and A); PS, psychosocial index (mean of SI, C, AB and EB); Overall, total SIP index (mean of all 12 categories). Differences between groups were tested by Fisher's non-parametric permutation test. ****P < 0.0001; ***P < 0.001; **P < 0.01; *P < 0.05; NS, not significant.

(b) Effect sizes of SIP categories and indexes for severely obese subjects (SOS) vs. unselected cancer survivors. Effect size was calculated as the mean scale score difference between groups divided by the pooled standard deviation

Figure 33.6(a) Mean scores of SIP categories and indexes for severely obese subjects (SOS) vs. unselected cancer survivors. High scores on SIP categories and indexes represent dysfunction. BCM, body care and movement; M, mobility; A, ambulation; SR, sleep and rest; E, eating; HM, home management; W, work; RP, recreation and pastimes; SI, social interaction; C, communication; AB, alertness behaviour; EB, emotional behaviour; PH, physical index (mean of BCM, M and A); PS, psychosocial index (mean of SI, C, AB and EB); Overall, total SIP index (mean of all 12 categories). Differences between groups were tested by Fisher's non-parametric permutation test. ****P < 0.0001; ***P < 0.001; **P < 0.01; *P < 0.05; NS, not significant.

(b) Effect sizes of SIP categories and indexes for severely obese subjects (SOS) vs. unselected cancer survivors. Effect size was calculated as the mean scale score difference between groups divided by the pooled standard deviation

Table 33.4 Obesity-related psychosocial problems (OP) in everyday life in severely obese men and women. Answers to the question: 'Are you bothered because of your obesity as regards the following activities?' (Scale range: definitely not bothered, not so bothered, mostly bothered, definitely bothered)

Percentage mostly or definitely bothered

Total

Total

Items in OP scale

Men

Women

Men

Women

Men

Women

Men

Women

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