14 May 2008
Energy Envelope Theory and CFS
Source: American Association of Occupational Health Nurses (AAOHN) Journal
Vol 56, pp. 189-195
Date: May 2008 URL: http://www.aaohn.org/practice/journal
The energy envelope theory and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome
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Leonard Jason Ph.D., DePaul University(*) Kathleen Muldowney, University of Wisconsin, Madison Susan Torres-Harding Ph.D, Roosevelt University
* Address correspondence to Leonard A. Jason, Ph.D., DePaul University,
Center for Community Research, 990 W. Fullerton Ave., Chicago, Il. 60614.
(email: Ljason@depaul.edu).
The authors appreciate the funding provided by NIAID (grant number AI 49720).
Abstract
Individuals with Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) have little stamina and endurance, and pose a challenge for care by nursing professionals. One theory that might be particularly useful in working with clients with ME/CFS is the Energy Envelope, which posits that maintaining expended energy levels at the same level as available energy level, may help reduce the frequency and severity of symptoms. In this study, a daily energy quotient was established by dividing expended energy level by perceived energy level and multiplying by 100. Findings are congruent with the Energy Envelope Theory as the daily energy quotient was related to a number of indices of functioning including depression, anxiety, fatigue, pain, quality of life, and disability. The overall results provide support for a way that health care professionals can work with clients with ME/CFS.
The energy envelope theory and Myalgic Encephalomyelitis/chronic fatigue syndrome
People with Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) generally experience sharp decreases in energy levels, which lead to a need to reduce physical activity (Friedberg & Jason, 1998). Often referred to as CFS, Fukuda et al. (1994) provided an international case definition that has been used to define this illness. The low energy levels can have a range of devastating effects. For example, sometimes people with ME/CFS are too fatigued to perform simple daily activities like housecleaning or carrying groceries. In many cases, they have to cut back the time they spend at work or even stop working altogether (Pesek, Jason, & Taylor, 2000).
Inconsistency of energy levels is another characteristic of people with ME/CFS, as they report dramatic changes between good and bad days (Friedberg & Jason, 1998). However, the variations in energy levels are often unpredictable, which makes it difficult to plan when one will be able to engage in physical activity or social interaction. In addition, increased fatigue and symptom severity are possible consequences of expending energy beyond the low energy levels (Jason, Melrose, et al., 1999). For example, on a day where peoples' energy level is higher than usual, the individuals may take advantage of it by expending extra energy, whether physical or mental, to compensate for any activities or work they were unable to do in periods of extremely low energy. This brief period of high expended energy levels is often followed by a "crash" or extended period of severe fatigue. Thus, people with ME/CFS find themselves in a repetitive cycle. Therefore, few who are afflicted by this syndrome experience a full recovery (Wilson et al., 1994).
Researchers disagree on the appropriate activity levels for people with ME/CFS. Some have hypothesized that symptoms are worsened by activity avoidance (Butler, Chalder, Ron, & Wessley, 1991). Butler et al.'s model suggests that people with ME/CFS reduce their activity levels in response to the fatigue or other symptoms brought on by some viral or bacterial infection. This results in a state of "learned helplessness." As individuals continue to avoid activity, their symptoms persist and may increase in severity due to a decrease in activity tolerance and an increase in sensitivity to any kind of stimulation (Butler, et al.). Conversely, Black, O'Connor, and McCully (2005) found that when individuals with ME/CFS were asked systematically to increase their daily physical activity by 30 percent, their overall mood, muscle pain intensity, and time spent with fatigue each day worsened. The exercise protocol in this study called for participants to increase their activity levels by walking every day while attempting to maintain all other regular daily activities. Because there were no "rest days" provided in this protocol, it is possible that they were approaching a daily activity limit. An additional finding was that not all participants with ME/CFS could attain a 30 percent increase in activity, and the level of increase was inversely related to the persons' baseline activity levels.
Those with the lowest baseline activity levels were able to maintain the largest increase and those with the highest baseline activity levels experienced a smaller increase (Black, et al., 2005).
Some have proposed that pacing of activities may be an effective way of coping with limited energy (Friedberg & Jason, 1998; Goudsmit, 2001).
However, the appropriate levels of activity and rest will vary depending on the unique condition of each individual. The concept of activity pacing is compatible with the Energy Envelope Theory (Jason, Melrose, et al., 1999), which has the goal of finding balance between the extremes of total avoidance of activity and high levels of increases in daily activity. The Energy Envelope Theory provides a way to manage ME/CFS. This theory suggests that by maintaining expended energy levels within the "envelope" of perceived energy levels, clients will be better able to sustain physical and mental functioning while reducing symptom severity and the frequency of relapses.
Individuals with ME/CFS who use this approach need to assess their perceived energy levels, i.e. available energy, on a daily basis and use that level to gauge their energy expenditure for the day. Applying this approach as a ME/CFS management tool involves accepting and working within the limits imposed by the disease rather than fighting against them. Over time, individuals may find that they experience fewer crashes and decreased fatigue and symptom severity. It may even be possible that by maintaining energy levels in this way, clients may be able to expand their envelope, that is, their perceived energy levels may increase over time, allowing them to engage in higher levels of physical activity. There is anecdotal support for this theory from the client community.
Few empirical studies have been conducted to assess the effectiveness of the Energy Envelope Theory. One case study wherein one participant made daily ratings of her perceived energy level, expended energy, and fatigue level on a 1-100 scale found that when she kept her expended energy levels within the envelope of her perceived energy levels, not only was her fatigue lower but her perceived energy tended to be higher (Jason, Melrose et al., 1999). A similar study that used time series regression found that there was a positive significant relationship between current fatigue level and self-rated expended energy two-days ago (Jason, Tryon, et al., 1999). The same study also took hourly ratings of perceived and expended energy and fatigue levels and found that the number of hours worked five days ago was negatively and significantly related to current fatigue. A third study (Pesek, et al., 2000) found that when participants with ME/CFS were provided with a buddy to reduce activities and to assist in identifying and reducing discrepancies between perceived and expended energy, overall fatigue severity as well as severity ratings for five of eight minor ME/CFS symptoms decreased. This finding was not statistically significant, likely due to the small sample size, but the directional trends were consistent with the Envelope Theory. While the studies above are limited by small sample sizes, the directional trends warrant a further look at this phenomenon and its possibilities as a tool for managing ME/CFS.
In the current study, the relationship between a daily energy quotient and self report measures tapping a wide variety of areas of functioning were assessed. It was predicted that exceeding perceived energy levels would be significantly correlated with more severe fatigue, greater symptom severity, and lower levels of physical and mental functioning.
Method
Participants
Participants with ME/CFS were recruited from a variety of sources, including physician referrals, announcements in local newspapers, and recruitment offers at local ME/CFS support group meetings. One hundred and fourteen individuals were recruited. Of the 114 individuals, 46 percent were referred by physicians, 34 percent were recruited by media (newspapers, TV, radio, etc.), and 20 percent stemmed from other sources (e.g., heard about the study from a friend, family member, person in the study, etc.). There were no significant demographic differences for individuals recruited from these varying sources. Twenty-four additional individuals who were screened were excluded due to a variety of reasons (i.e., lifelong fatigue, less than four Fukuda symptoms, BMI > 45, melancholic depression or bipolar depression, alcohol or substance abuse disorder, autoimmune thyroiditis, cancer, lupus, rheumatoid arthritis). Approaches to reduce attrition included use of letters and telephone reminders of all appointments, flexibility regarding working around vacations and medical and other crises, reimbursement for transportation costs, and participant honoraria.
Procedure
All participants were required to be at least 18 years of age, not pregnant, able to read and speak English, and considered to be physically capable of attending the scheduled sessions. Bedridden and wheelchair bound individuals were excluded due to the practical difficulties of making appointments.
Referrals to local physicians who treat ME/CFS and to support groups were offered to these individuals. After a consent form was filled out, prospective participants were initially screened, using a structured questionnaire. Next, a semi-structured psychiatric interview was administered.
Measures
The Structured Clinical Interview for DSM-IV (SCID) (Spitzer, Williams, Gibbon, & First, 1995). Axis I was used to establish psychiatric diagnoses.
The professionally administered SCID allows for clinical judgment in the assignment of symptoms to psychiatric or medical categories, a crucial distinction in the assessment of symptoms that overlap between ME/CFS and psychiatric disorders (e.g., fatigue, concentration difficulty, and sleep disturbance).
The CFS Questionnaire.
This screening scale was initially validated by Jason et al. (1997). This scale was used to collect demographic, health status, medication usage, and symptom data, and it uses the definitional symptoms of ME/CFS as defined by Fukuda, et al. (1994). Hawk, Jason, and Torres-Harding (2007) recently revised this ME/CFS Questionnaire, and administered the questionnaire to three groups: those with ME/CFS, those with Major Depressive Disorder, and healthy controls. The revised instrument, which was used in the present study, evidences good test-retest reliability and has good sensitivity and specificity. Each of the eight Fukuda, et al. (1994) symptoms (e.g., post- exertional malaise, unrefreshing sleep, etc.) were rated on a 100 point-scale, with higher scores indicating more severe symptoms.
The CFS Questionnaire was designed to assess the diagnostic criteria for ME/CFS as specified by Fukuda, et al. (1994). For each symptom, participants were asked to indicate if the symptom had been present for six months or longer, if the symptom began before the onset of their fatigue or health problems, and how often (never, seldom, often/usually, or always) the symptom is experienced. Participants were also asked to rate the intensity of each symptom they endorsed on a scale of 0 to 100, where 0= no problem and 100= the worst problem possible. To measure the Fukuda, et al. (1994) case definition symptoms, items were designed to measure the presence of the eight minor symptoms (i.e., impaired memory or concentration, sore throat, tender lymph nodes, muscle pain, multi-joint pain, new headaches, unrefreshing sleep, and post-exertion malaise) as specified by the Fukuda, et al. case definition. Two other items assessed the frequency with which participants avoid exercise, as rated on a five point scale where 1= never, and 5= all the time, and participants' rating of the degree to which fatigue has impaired daily energy levels, on a 1-10 scale, with higher scores indicating higher impairment.
Medical Assessment of ME/CFS.
The medical screening evaluation included an in-depth medical and neurological history, as well as general and neurological physical examinations. The evaluation also included a structured instrument, a modified version of the CFS questionnaire (Komaroff, et al., 1996). This instrument assesses the signs, symptoms, and medical history to rule out other disorders. Relevant medical information was gathered to exclude possible other medical causes of chronic fatigue, including exposure histories to tuberculosis, AIDS, and other sexually transmitted diseases.
Information on prescribed and illicit drug use was also assessed and recorded. With women, results of recent Pap smears and mammograms were obtained. Finally, the history of all symptoms related to ME/CFS was gathered.
Laboratory tests in the battery were the minimum necessary to rule out other illnesses (Fukuda, et al., 1994). Laboratory tests included a chemistry screen, which assesses liver, renal, and thyroid functioning; complete blood count with differential and platelet count, erythrocyte sedimentation rate; arthritic profile, which includes rheumatoid factor and antinuclear antibody; hepatitis B; Lyme Disease screen; HIV screen; and urinalysis. A tuberculin skin test was also performed. The project physician performed a detailed medical examination to detect evidence of diffuse adenopathy, hepatosplenomegaly, synovitis, neuropathy, myopathy, cardiac or pulmonary dysfunction.
Beck Depression Inventory (BDI-II) (Beck, Steer, & Brown, 1996).
Depressive symptomatology was measured with the BDI-II, a 21-item self-report instrument with well-established psychometric properties. This version of the BDI is more consonant with DSM-IV criteria for major depressive disorder.
The BDI-II is the only depression rating scale to be empirically tested and interpreted for both depressed and non-depressed clients with ME/CFS (Johnson, DeLuca & Natelson, 1996). Higher scores indicate more depression.
Beck Anxiety Inventory (BAI).
Anxiety symptoms were measured with the BAI, a 21-item self-report measure with established and replicated construct validity (Steer, Clark, Beck, & Ranieri, 1995). Factor analysis of the BAI and BDI yielded a first-order factor labeled anxiety that had salient loadings for all 21 items on the BAI, but only one item on the BDI. Also, there is a high frequency of anxiety disorders reported in psychodiagnostic studies of ME/CFS (Pepper, Krupp, Friedberg, Doscher, & Coyle, 1993). Higher scores indicate more anxiety.
Fatigue Severity Scale (FS) (Krupp, LaRocca, Muir-Nash, & Steinberg, 1989).
This scale was used to measure fatigue. This scale includes nine items rated on seven- point scales and is sensitive to different aspects and gradations of fatigue severity. Most items in the Krupp fatigue scale are related to behavioral consequences of fatigue. Previous findings have shown the scale can discriminate between individuals with ME/CFS, MS, and primary depression (Pepper et al., 1993). In addition, the Fatigue Severity Scale (Krupp, et al., 1989) was normed on a sample of individuals with MS, SLE, and healthy controls. A study by Taylor, Jason, and Torres (2000) compared the Fatigue Scale (Chalder, Berelowitz, Pawlikowska, Watts, & Wessely, 1993) with the Fatigue Severity Scale (Krupp, et al., 1989) with a sample of healthy controls and a ME/CFS-like group. Within a ME/CFS-like group, the Fatigue Severity Scale (Krupp, et al., 1989) was more closely associated with severity ratings for the eight Fukuda, et al. (1994) ME/CFS symptoms as well as with functional outcomes related to fatigue. Higher scores indicate more fatigue.
Perceived Stress Scale (PSS) (Cohen, Kamarck, & Mermelstein, 1983).
This is a four-item revised version of a previous 14-item measure of global perceived stress. The time period that this instrument measures is the previous month. The authors report a coefficient alpha reliability of .72 for the four-item short version. The Total Stress score was used in the present study. It has a range from 0-16, with higher scores measuring more stress.
Brief Pain Inventory (Cleeland & Ryan, 1994).
This instrument was administered to measure the intensity of pain (pain
severity) and the interference of pain in the individuals' life (pain interference). Higher scores indicate more severe levels of persistent pain and higher levels of interference with functioning. This measure exhibits adequate levels of reliability to assess pain in noncancer samples, with coefficient alphas of .70 and above. It also evidences good concurrent validity with other generic pain measures, and has been shown to be sensitive to changes in pain status over time (Keller, Bann, Dodd, Schein, Mendoza, & Cleeland, 2004).
The Pittsburg Sleep Quality Index (Buysse, 1989).
Sleep disturbances were examined by using this index, which was developed to measure sleep quality in psychiatric research It measures sleep disruptions and sleep quality. There are nineteen questions, on scales from zero to three, which generate seven "component" scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The sum of scores for these seven components yields one global score, which can range from 0 to 21, with higher scores indicating worse sleep quality.
The Quality of Life Scale (Burckhardt & Anderson, 2003).
This measures satisfaction with different life activities for individuals with various chronic illnesses. The scale consists of 16 items answered on a Likert type scale, from one to seven, which measures six conceptual domains of quality of life: material and physical well-being, relationships with other people, social, community and civic activities, personal development and fulfillment, and recreation, and independence. Higher scores mean more overall life satisfaction. This instrument differs from most other measures in its acknowledgement that individuals place different priorities on different aspects of life quality. This scale demonstrated high test-retest reliability for this 16-item scale, and convergent and discriminate construct validity in groups of individuals with various stable chronic illness, including post-ostomy surgery, osteoarthritis, rheumatoid arthritis, fibromyalgia, COPD, and insulin-dependent diabetes (Burckhardt & Anderson, 2003).
Self Efficacy.
This is a measure of how much control a person feels with respect to ME/CFS complaints. The ratings from each of the five questions are added.
Cronbach's alpha reliability range from .70 to .77, and the scale has been used in one of the major trials involving ME/CFS and CBT (Prins, et al., 2001). Higher scores indicate higher levels of self-efficacy.
Medical Outcomes Study-Short Form-36 (SF-36) (Ware & Sherbourne, 1992).
This 36 item broadly-based self-report measure of functional status related to health, identifies eight health concepts as perceived by the individual.
The concepts include Physical Functioning, Role Functioning-Physical, Role Functioning-Emotional, Bodily Pain, General Health, Vitality, Mental Health, and Health Transition. Test construction studies (McHorney, Ware & Raczek, 1993; McHorney, Ware, Lu, & Sherbourne, 1994) have shown adequate internal consistency, significant discriminate validity among subscales, and substantial differences between patient and non-patient populations in the pattern of scores. It also has indicated sufficient psychometric properties as a measure of functional status in a ME/CFS population (Buchwald, Pearlman, Umali, Schmaling, & Katon, 1996). A behavioral treatment study of ME/CFS clients showed that the SF-36 is sensitive to treatment changes (Deale, et al., 1997). A higher score indicates better health and functioning.
Perceived and Expended Energy.
Participants were asked to rate perceived energy and expended energy over the past 24 hours on a 100-point scale, with 0= no energy and 100= abundant energy similar to when the person was completely well. Fatigue was also rated on a 100-point scale, with higher scores indicating higher fatigue over the past 24 hours. Hawk, Jason, and Torres-Harding (2007) found test-retest reliability for perceived energy, expended energy, and fatigue to be .73, .50, and .84, respectively. Perceived Energy referred to the participants'
estimation of their available energy resources. Expended Energy was defined as the participants' estimation of the total amount of energy exerted.
Expended Energy can be greater than Perceived Energy, particularly when participants push themselves over their energy limits. The percentage of Available Energy expended was derived by dividing the participants' Expended Energy by their Perceived Energy. This number was then multiplied by 100.
This represents the Daily Energy Quotient. Numbers below 100 indicated that the participants expended less than their perceived maximum available energy, whereas numbers above 100 indicated that the participants expended more energy than their perceived maximum available energy.
Results
Of 114 participants, four participants were excluded because of incomplete data (more information on sociodemographic characteristics of this sample as well as procedures is described elsewhere, Jason, et al., 2007). The Daily Energy Quotients range from a minimum of 50 to a maximum of 5,667 (one individual's expended energy was 85 and his perceived energy was 1.5, and therefore dividing his expended by perceived energy resulted in a score of 56.67, and multiplying by 100 increased the score to 5,667). The average score was 339 (SD=685), 13.6 percent of the sample had a Daily Energy Quotient below 100; 86.4 percent had a Daily Energy Quotient above 100.
Given
the skewed distribution of the sample, Spearman's Rank Order Correlation was used to calculate the strength of the relationship between variables.
There was a strong positive correlation between the Daily Energy Quotient and the daily (past 24 hours) fatigue rating [r(N=110 )=.56, p<.01] with higher Daily Energy Quotients associated with higher daily fatigue ratings. Of the eight Fukuda symptoms examined, only post-exertional malaise was significantly related to the Daily Energy Quotient [r(N=110)=.22, p<.05]. Higher Daily Energy Quotients were associated with higher severity ratings for this symptom.
Table 1 presents the results of Spearman's Rank Order Correlational analysis of the Daily Energy Quotient and participants' scores on various self-report measures. All significant results were in the expected direction. Higher Daily Energy Quotients were associated with higher levels of depression, anxiety, fatigue severity, and sleep problems. Higher Daily Energy Quotients were also associated with worse quality of life. Higher Daily Energy Quotients were associated with lower levels of physical functioning, and lower levels of vitality. Higher Daily Energy Quotients were also associated with more problems with work or daily activities.
There was also a significant positive correlation between Daily Energy Quotients and the frequency with which participants avoided exercise [r(N=108)=.20, p<.01]. High Daily Energy Quotients were associated with greater frequency of exercise avoidance. Daily Energy Quotients also had a significant positive relationship with participants' rating of the degree to which fatigue impaired daily energy levels [r(N=109)=.34, p<.01]. High Daily Energy Quotients were associated with higher levels of impairment.
Discussion
Overall the results are compatible with the Energy Envelope Theory, which is an extremely helpful construct for health care workers. The present study found that the Daily Energy Quotient was related to a number of indices of functioning including depression, anxiety, fatigue, pain, quality of life, and disability. The findings suggest that individuals with ME/CFS experience a range of negative symptoms and disability when they extend beyond their energy envelope. In other words, being over-extended,(i.e., exerting more energy than they had available) was associated with encountering more difficulties in a variety of areas. Certainly, this has implications for the clinical care of patients with this illness.
From the Energy Envelope Theory (Jason, Melrose et al., 1999), nurses might help individuals with ME/CFS pace their activity according to their available energy resources. In this approach, the phrase, "staying within the envelope," is used to designate a comfortable range of energy expenditure, in which an individual avoids both overexertion and underexertion, maintaining an optimal level of activity over time. Findings from the present study would support this assertion. The Energy Envelope Theory would not endorse recommendations to either unilaterally increase or decrease activity. Some people with ME/CFS need to be encouraged to increase their activity, when they have the appropriate amount of perceived energy to do so. However, there are also people with ME/CFS that need to be encouraged to do less in order to decrease the discrepancy between perceived and expended energy. This theory emphasizes the need to understand the differential needs of subtypes of individuals with ME/CFS. The key is to not overexpend their energy supplies or consistently go outside their "envelope" of available energy. Once this has been accomplished, it would then be possible to slowly increase the amount of activity they might engage in (King, Jason, Frankenberry, & Jordan, 1997; Pesek, et al., 2000). Rather than focusing on a cure, this approach focuses on improving the ability of clients to cope with this illness, and tailored interventions by nurses and other health care professonals are needed for the unique needs of different subgroups of clients.
It might be possible to suggest a link between overexerting oneself and the exacerbation of symptoms and disability. Miller and Cohen (2001) proposed that negative emotional responses are due to evaluating stressful experiences as a significant threat and as exceeding available coping resources. They also cited studies suggesting that these negative emotional responses can cause distressed clients to engage in behaviors (e.g., altering sleep patterns, alcohol and tobacco use, or decreasing physical activity) which conceivably modify immune responses. In addition, negative emotional states might activate the sympathetic division, whose fibers, descending from the brain to lymphoid tissues such as bone marrow, thymus, spleen, and so forth, could release substances that influence immune responses. Distress also can activate the Hypothalamus-Pituitary- Adrenal axis and hormonal products from these systems can dysregulate the immune system. It is possible that when clients go beyond their energy envelopes it is a stressful experience, and it contributes to the behavioral, sympathetic, and immune dysregulations of individuals with ME/CFS.
Study Limitations
The findings in the present study should be tempered with caution as all measures were based on self-report data. Clearly, there is a need to introduce more behavioral objective data from actigraphs or more biological data in future studies. In addition, the Daily Energy Quotient is a result of estimates of hypothetical constructs, and there might be certain errors that can occur in trying to estimate the extent of perceived or expended energy within a particular 24 hours. Also, the extent of going beyond one's energy envelope might vary from day to day, and this is another limitation in the study. Finally, the correlations tended to be low, and thus much of the variance was not being accounted for.
Even with these limitations, the present study does support that the anecdotal information supplied by individuals about the relationship between being overextended and exacerbation of symptoms. Future research in this area might examine longitudinal data sets to determine whether energy expenditures can be predictors of long term outcomes for individuals with ME/CFS (Jason, & Choi, 2008). Additional research is also warranted examining the relationships between energy quotients and more biological measures of functioning.
Implications for Occupational Health Nurses
Severe fatigue is a common compliant of patients seeking care from Occupational Health Nurses and other health care workers. For too long, these symptoms have been not well understood and as a result, clients have often not been provided adequate care for their presenting problems. Those that ME/CFS have six or more months of severe fatigue and other debilitating symptoms, and they represent an even more chronically ill group.
Occupational Health Nurses have an important role to play with such clients.
When clients present to health care settings with ME/CFS, it is important to provide such clients with tailor made interventions that take the unique needs of such clients into account. Occupational Health Nurses have unique roles to play in helping to develop and implement a treatment plan for such clients. In addition to helping to coordinate comprehensive planning, Occupational Health Nurses can consider the Energy Envelope a useful treatment approach when working with clients diagnosed with ME/CFS. By working with clients to help them find ways to stay within their Energy Envelopes, the clients will respond better to interventions and there might be symptomatic relief from some of the more severe complaints that patients experience.
Table
Table 1. Spearman correlation coefficients for daily energy quotient and
self-
report measures
----------------------------------------------------------------------------
--
Daily Energy Quotient
(N=110)
----------------------------------------------------------------------------
--
BDI-II (depression)^a .27**
BAI (anxiety)^a .23*
Fatigue severity scale (fatigue)^a .22*
Perceived stress scale (stress)^a .14
Brief pain inventory (pain)^a .21**
Pittsburgh Sleep Quality Index (sleep problems)^a .25*
Self-efficacy scale (self-efficacy)^b .05
Quality of life scale (quality of life)^b -38**
SF-36
Physical functioning (functioning)^b -.21*
Role-physical (problems with daily activities)^b -.20*
Bodily pain (pain)^b -.15
General health (health)^b -.15
Vitality (vitality)^b -.22*
Social functioning (interference in function)^b -.18
Role-emotional (emotional functioning)^b -.17
Mental health (nervousness and depression)^b -.19
----------------------------------------------------------------------------
--
^a Higher scores mean more problems or worse functioning ^b Higher scores mean less problems or better functioning
* p<.05
** p<.01
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