Memory for Fatigue proven accurate

International Journal of Behavioral Medicine Vol. 15, #1, pp. 29-33 January 2008 http://www.informaworld.com/smpp/title~content=t775653652~db=all

Memory for fatigue in Chronic Fatigue Syndrome: the relation between weekly recall and momentary ratings

Fred Friedberg and Stephanie J. Sohl - Department of Psychiatry and Behavioral Science, Stony Brook University, Stony Brook, NY. * Correspondence concerning this article should be addressed to Fred Friedberg, Ph.D., Department of Psychiatry and Behavioral Science, Putnam Hall/South Campus, Stony Brook University, Stony Brook, NY 11794-8790, USA. E-mail: fred.friedberg@stonybrook.edu

Patients with chronic fatigue syndrome (CFS), a disabling illness of unknown etiology (Fukuda et al., 1994) report persistent severe fatigue, although their daily fatigue patterns may show considerable variation (Stone et al., 1994; Wood, Magnello, & Sharpe, 1992). Thus, complaints of "always" being extremely fatigued may indicate recall of higher or more enduring fatigue than was actually experienced (Wood et al.,1992). Furthermore, the cognitive theory of CFS (Surawy, Hackman, Hawton, & Sharpe, 1995) argues that the patient's (erroneous) suspicion of disease heightens symptom perception and distress which amplifies symptoms and reinforces the belief that the sufferer is sick.

Given the above considerations, it would be important for both health practitioners and clinical researchers who evaluate CFS to know if their patients' recall of fatigue is discrepant with their daily symptom experiences. An initial study on memory for fatigue in COPD patients (Meek, Lareau, & Anderson, 2001) over a 14-day period found very high levels of agreement between recall and real-time daily fatigue intensity ratings, with no significant differences between the two types of measurement. However, this study used paper diaries returned at the end of the data collection period.

Paper diaries have shown sharply lower compliance with scheduled data entry times in comparison to electronic dairies (Stone & Shiffman, 2002). For instance, diary entries for a one-week data collection period may be done on the last day of data collection as opposed to their scheduled daily times. Such non-compliance may cast doubt on the validity of memory studies using paper diaries without confirmation procedures.

To address the issue of confirmation of symptom ratings in vivo, a recent memory study of patients with chronic pain (Stone, Broderick, Shiffman, & Schwartz, 2004) recorded multiple daily pain ratings in time-stamped electronic diaries followed by weekly recall of pain over a two-week period. These authors found that weekly recall of pain intensity was significantly higher than momentary ratings, although recall agreement between weekly and momentary ratings was moderate to high.

Current Study

The goal of this study was to assess memory for symptoms in participants with CFS. We hypothesized that between-person associations between momentary ratings and weekly recall of fatigue would be moderate to high. These findings may have implications for the conduct of office examinations for CFS.

Methods

Participants

The participants were 71 adults with CFS, recruited primarily from non-clinical sources as part of a larger naturalistic study using radio, TV, newspaper and newsletter advertising, CFS and fibromyalgia websites, physician referrals, and hospital announcements. There were no demographic differences among these sources of recruitment. Candidates were offered $100 compensation for participation. All participants signed consent forms approved by the Stony Brook University institutional review board.

Participants were diagnosed with CFS by the study physician or physician's assistant as supervised by the project physician. The diagnosis was based on the established criteria for CFS (Fukuda et al., 1994; Reeves et al., 2003) which included six months of medically unexplained, debilitating fatigue plus four out of eight secondary symptoms. In addition, the definitional criteria for CFS excluded patients who had identifiable medical and psychiatric conditions that might plausibly explain their fatigue symptoms. Psychiatric exclusions were based on the results of the Structured Clinical Interview for DSM-IV (First, Spitzer, Gibbon, & Williams, 2001) conducted by Friedberg or his graduate student (D.W. Leung).

Additional inclusion criteria were age requirements (18-60 years), English fluency, and wakefulness between 9 AM and 9 PM daily. Eight-hundred and forty-one telephone-screening interviews (conducted by Friedberg) yielded 231 candidates (27.4%) eligible for the study. Of these eligible patients, 126 (54.5%) agreed to participate. Participant withdrawal was largely due tothe time commitment involved in the larger study.

A final CFS diagnosis was confirmed in 123 (95.5%) of these participants, of which data for this study was available for 71 subjects. There were no demographic differences between the larger participant pool and the subset who participated in this study. The average age of the participants was 42.0 years (SD=8.6) and 85.3% were women. Participants were predominantly white (92.8%), highly educated (73.9% attending at least some college), and married or cohabitating (57.9%). The mean duration of the CFS illness was 8.03 years (SD=6.8; range: 0.75-37 years).

Measures and Materials

Momentary Measure: Electronic Diary. The electronic diary was a palm pilot computer (Model: Palm Vx, Palm Inc., Sunnyvale, CA 94085) with software (Satellite Forms, Palm Inc., Sunnyvale, CA 94085) specifically designed to record momentary data. The system has been successfully used in many other studies (e.g., Aaron, Turner, Mancl, Brister, & Sawchuk, 2005; Stone et al., 1994). The palm pilot emitted auditory prompts that were linked to a display of symptom rating scales. A participant-operated stylus was utilized to select a response to each numerical symptom scale. The software recorded the time and date of each entry. To avoid interruptions of important ongoing activities (e.g., business meetings), participants were allowed to enter data in between scheduled prompt times.

In order to obtain a representative diurnal sample of symptoms without undue subject burden (Stone & Shiffman, 2002), the palm pilots prompted subjects for 21 days, 6 times a day, every 2 hr plus or minus a randomly programmed 1 ­20 min interval (Stone & Shiffman, 1994). The first daily prompt occurred within 1 hr of the subject's wakening and the last daily prompt approximately 12 hr later. No prompt signals occurred during the subject's reported sleep time. After each prompt, a screen was displayed with a numerical rating scale (0 ­10) that was labeled "Fatigue Now." The end point anchors on the numerical scales were None (0) and Highest (10). Subjects were instructed to record intensity ratings on the numerical scale for their current levels of fatigue.

Recall Assessment of Symptoms and Affect. At the end of each week of momentary assessment, recall ratings of fatigue for that week were obtained from subjects via telephone. The format of the question asked was: "What was your average fatigue over the past7 days from 0 to 10, with 0 indicating 'none' and 10 indicating the 'highest'?"

Procedure Participants were trained individually on how to use the palm pilot and how to answer the electronic diary questions. Subsequently, the 3 weeks of momentary and recall data collection were completed.

Statistics Correspondence between Weekly and Momentary Reports of Fatigue. The statistical analyses used to compare recalled and momentary fatigue measures were based on a previous study on the recall of pain (Stone et al., 2004). T-tests were used to assess differences between momentary and recall fatigue ratings. In addition, consistency between weekly recall and average momentary reports of fatigue was measured with a Pearson correlation and two types of intraclass correlations: the ICC (C,1) and ICC (A,1). The Pearson correlation measures rank ordering but does not assess any differences in variability or level of absolute agreement between the two compared measures. The ICC (C,1) intraclass correlation addresses both consistency in ranking as well as adjusting for variability in the measures. The ICC (A,1) evaluates level of absolute agreement between the measures (Stone et al., 2004).

Results

Three weeks of momentary and weekly recall data were available for analysis. Participant compliance with the palm pilot prompts was excellent: The average compliance rate for the full sample over the three week data collection period was 92% (week 1: 94%; week 2: 92%; week 3: 91%). Three-week average compliance rates for individual participants ranged from 71-100%. Only three subjects had compliance rates below 80%. The means and standard deviations for average momentary and recalled fatigue and pain are presented in Table 1.

Average three-week ratings for recall of fatigue were about 0.4 of a point higher (8.5%) than average momentary fatigue scores on an 11-point scale (0-10). Large absolute differences between recall and momentary and recall ratings were uncommon. Over the three weeks of data collection, only 7.0% of participants recalled fatigue ratings, on average, that were either 2 points or more higher or lower than their momentary ratings.

The overall differences in recall versus momentary ratings of fatigue were significant for all three weeks (week 1: t(62)=-3.77, p<0.001; week 2: t(64)=-2.02, p<0.05; week 3: t(61)=-3.02, p<0.01). The corresponding effect sizes (d; Cohen, 1988) were small:0.38 (week 1), 0.21 (week 2), and 0.25 (week 3).

Consistency and Agreement

The Pearson correlations (Table 2) between recall and momentary ratings, the first measure of consistency for fatigue, were significant for all three weeks. This indicates that participants who rated momentary fatigue higher also recalled higher levels of fatigue. The ICC (C,1) analysis also revealed significant associations, reflecting the fact that the variances of the two fatigue measures were similar. The absolute agreement ICCs (A,1) were somewhat lower, indicating that participants recall ratings shared about 50% of the variance with their absolute levels of momentary fatigue.

Discussion

This study examined the degree of consistency and agreement between weekly recall and average momentary ratings of fatigue as reported over a three-week period in patients with CFS. Our hypothesis was confirmed: correlations between real-time momentary reports and weekly recall of fatigue intensity were moderate to high.

Consistency and Agreement

Overall, these findings for fatigue symptoms were similar to the results of memory studies in chronic pain. The Pearson and consistency correlations between weekly recall and momentary reports of fatigue were slightly higher than the recall agreement correlations, consistent with previous research on chronic pain (Bolton, 1999; Stone et al., 2004). In the current study, the fatigue recall ratings were significantly higher than momentary ratings for all three weeks of data collection, although the average effect size was small.

One possible explanation for the discrepancy between recall and momentary ratings is sampling error. Because momentary ratings were based on a limited number of samples from each day, unrecorded ratings that the participant would have accurately recalled may have been missed. However, previous studies using experience sampling methodologies have found higher pain levels (Stone et al., 2004), more intense emotions (e.g., Parkinson, Briner, Reynolds, & Totterdell, 1995; Thomas & Diener, 1990) and more severe marital disagreements (e.g., McGonagle, Kessler, & Schilling, 1992) in retrospective as compared to concurrent reports. If different subjective criteria, particularly salience, are involved in retrospective versus real-time reports, then higher symptom ratings may be associated with longer recall periods.

Clinical Applications

Understanding how patients with CFS recall their fatigue is important because symptom severity is an essential clinical dimension of this poorly understood illness, which lacks biological indictors for diagnosis. Our findings that CFS patients' recall of fatigue was in moderate to high agreement with the fatigue they actually experienced in their home environments can provide at least some level of validation to clinicians of the reality of their patients' symptom complaints. Unlike the assertion of Wood et al. (1992) that CFS patients "always" report being extremely fatigued, the data in this study revealed that patients' fatigue levels, for both momentary and recall experience, averaged out at moderate intensity levels.

The symptom amplification model of functional somatic syndromes (Barsky & Borus, 1999; Shorter, 1992) which has found application in a cognitive model of CFS (Surawy et al., 1995) may have been modestly confirmed in this study because symptom recall was significantly higher than momentary symptom intensity. Yet it seems implausible that the relatively minor overestimation of symptom intensity, given the small effect sizes, would account for the disabling symptoms of CFS.

Alternatively, symptom amplification, if present, may operate more prominently on either the momentary symptom experience itself or the more general trait-like perception of personal fatigue, rather than on weekly symptom recall. Catastrophizing has been associated with in vivo average daily pain intensity in a study of chronic pain patients (LeFebvre & Keefe, 2002). Furthermore, trait-like fatigue and impairment have been found to be related to catastrophizing in CFS patients (Petrie, Moss-Morris, & Weinman, 1995) and may be one mechanism of symptom amplification (Barsky & Borus, 1999).

This study is limited by the absence of a control condition of healthy or fatigued subjects (without CFS) that would help to ascertain if the recall discrepancy findings were specific to CFS. Given the above findings in chronic pain, it may be that people with symptoms generally amplify their retrospective recall of their symptoms. In addition, this study was conducted on a largely non-clinical sample with a low percentage of minority subjects in comparison to the much higher percentages of minorities found in a population study in CFS (Jason et al., 1999).

For future research, the relationship of the theoretical construct of symptom amplification as it pertains to CFS could be explored with respect to momentary and recalled symptoms using measures of catastrophizing and negative affect. Future studies might also manipulate recall in a controlled experimental setting, for instance, by exploring different periods of time for recall to see how this influences the level of recall agreement.

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