Distinguishing between frequency and intensity of health-related symptoms from diary assessments
Introduction
Interest in self-reported somatic and affective symptoms is high in research, clinical, and health policy settings. Knowledge about health-related symptoms is important for evaluating health care and treatment, for understanding health disparities, and for tracking population trends in health and wellbeing over time [1], [2]. To date, two characteristics of symptom experience – their frequency and their intensity – have often been overlooked or simply combined into single measures, in part, because there has been limited empirical study of the distinction [3]. The question addressed here is whether symptom frequency and intensity should be viewed and can be measured as distinctive health outcomes.
There are compelling conceptual arguments for separating the frequency and intensity of symptom experiences. A person could have symptoms of pain, fatigue, or emotional distress at mild levels yet very often, whereas another person could have symptoms at high levels but only occasionally, as in the case of symptom flares. The overall symptom severity (i.e., its average magnitude across time) could be very similar for both people, despite pronounced differences in the composition of symptom frequency and intensity. Discriminating these patterns could have implications for practice and research, perhaps suggesting different mechanisms and indicating different treatment strategies [3], [4].
Despite its theoretical appeal, the frequency–intensity distinction has received little empirical justification in past research on self-reported somatic symptoms. Chang et al. [3] compared retrospective self-report ratings of fatigue using a frequency (none of the time–all of the time) or intensity (not at all–very much) response format and found that the two produced largely corresponding scale scores (correlation of .86). Similarly, scales that ask participants to rate either the frequency (not at all–almost always) or intensity (not at all–extremely) of posttraumatic stress disorder symptoms have been found to yield highly overlapping information (correlation of .93) [5]. Based on these findings, it has been argued that the concepts are virtually redundant and that there is little use in querying frequency and intensity of somatic symptoms separately [3], [4], [5].
Importantly, however, these studies examined retrospective questionnaires, where respondents were asked to summarize their symptoms over several days (e.g., the past 7 days)[3]. Recall ratings can be impacted by memory biases [6], and contextual factors can influence how people use and interpret frequency and intensity response scales in retrospective self-reports [7]. Symptom diaries, such as ecological momentary assessment (EMA) and the Day Reconstruction method (DRM), mitigate or eliminate the effects of recall bias [6], [8]. In addition, by collecting experience ratings across multiple moments or episodes, outcome measures that summarize these experiences are created by the researcher and not implicitly by the respondents. In other words, measures of symptom frequency and intensity can be directly computed from the diary data instead of relying on the participant's ability to meaningfully map their experiences onto a response scale that queries either frequency or intensity [9].
The purpose of this study was to investigate whether symptom diaries allow for a reliable and useful distinction between the frequency and intensity of health-related outcomes. Data from a nationally representative sample of over 12,000 individuals collected by the 2010 American Time Use Survey (ATUS, http://www.bls.gov/tus/) were utilized. Similar to the DRM, respondents were interviewed about the prior day, provided a “chunking” of the day into distinct episodes, and rated their pain, tiredness, sadness, and stress for 3 selected episodes. We conceptualized the frequency of a symptom as the proportion of episodes in which it was endorsed as present, and its intensity as the average level of the symptom when it was present, consistent with prior related literature examining basic components of affect [10], [11], [12].
To evaluate the utility of the distinction, we examined the extent to which symptom frequency and intensity were differentially associated with demographic characteristics, notably, gender, age, income, and educational attainment. Insight into the prevalence of emotional and somatic symptoms across demographic groups is important for understanding of who is more likely to seek healthcare and to facilitate more cost-effective utilization of healthcare resources. However, it is important that the derived prevalence rates be as precise and informative as possible. Thus, the question we addressed here was whether separating frequency and intensity symptom components reveals demographic differences that are otherwise obscured.
Section snippets
Participants and procedure
Data collected as part of the US Bureau of Labor Statistics' 2010 ATUS project with addition of the NIA-supported Wellbeing Module (WBM) were used for this study. The main purpose of ATUS is to develop nationally representative estimates of how people spend their time based on a subset of households who recently completed the Current Population Survey (CPS). Respondents are interviewed over the telephone to provide a detailed time diary of the previous day. In a series of questions, the
Descriptive results
Health-related symptom data were available from 12,829 ATUS Wellbeing Module respondents. Participants provided symptom ratings for 38,059 diary episodes or an average of 2.97 episodes per person, slightly less than the targeted 3 episodes per person (1.1% responses were missing). The mean episode length was 67 min (SD = 96, range 5 to 1107 min). Fig. 2 shows the response distribution for pain, tired, sad, and stress. As can be seen, the distributions were heavily skewed with a large proportion of
Discussion
The results of this study support the distinction between the frequency and intensity of health-related symptoms in the context of a multi-episode, diary-based assessment method. Both symptom components could be captured with reasonably good reliability of > .70 based on no more than 3 diary episodes collected in the ATUS wellbeing module. Notably, the reliabilities were similar to those obtained when applying the traditional strategy of averaging the ratings, suggesting that decomposing symptom
Conflict of interest
A.A.S. is a Senior Scientist with the Gallup Organization and a Senior Consultant with ERT, Inc.
Acknowledgments
This research was supported by a grant from the National Institute on Aging (P30 AG024928; Stone, PI).
References (28)
- et al.
Understanding recall of weekly pain from a momentary assessment perspective: absolute agreement, between- and within-person consistency, and judged change in weekly pain
Pain
(2004) - et al.
Assessment of pain: a community-based diary survey in the USA
Lancet
(2008) - et al.
Measuring health-related quality-of-life
Ann Intern Med
(1993) - et al.
Patient reported outcome measures: a model-based classification system for research and clinical practice
Qual Life Res
(2008) - et al.
Should symptoms be scaled for intensity, frequency, or both?
Palliat Support Care
(2003) - et al.
Pain measurement in patients with low back pain
Nat Clin Pract Rheumatol
(2007) - et al.
Examining the uniqueness of frequency and intensity symptom ratings in posttraumatic stress disorder assessment
J Nerv Ment Dis
(2006) Retrospective and concurrent self-reports: the rationale for real-time data capture
- et al.
A survey method for characterizing daily life experience: the day reconstruction method
Science
(2004) - et al.
Expanding options for developing outcome measures from momentary assessment data
Psychosom Med
(2012)
Affect intensity: separating intensity and frequency in repeatedly measured affect
J Pers Soc Psychol
Emotional experience in everyday life across the adult life span
J Pers Soc Psychol
Intensity and frequency—dimensions underlying positive and negative affect
J Pers Soc Psychol
High income improves evaluation of life but not emotional well-being
Proc Natl Acad Sci U S A
Cited by (28)
The Effects of Being Informed About Chemotherapy-Related Cognitive Symptoms With And Without Self-Affirmation on Perceived Cognitive Symptoms of Breast Cancer Patients: A Randomized Prospective, Longitudinal Study
2022, Clinical Breast CancerCitation Excerpt :Potentially, symptom severity is a greater indication of the experienced symptom burden or distress and of the extent to which patients value their cognition than the prevalence of symptoms. In symptom research, frequency and severity are generally considered and included as separate but often related components of the symptom experience eg,71 but empirical study of their distinction,72 or the degree to which these and other components contribute to overall distress is limited.73 Hypothetically, some components contribute to distress more than others and are therefore more sensitive to stress-reducing interventions.
Central sensitization has major impact on quality of life in patients with axial spondyloarthritis
2022, Seminars in Arthritis and RheumatismCitation Excerpt :While reasons for these differences are still largely unclear, hormonal differences may play a role in pain processing [31]. Perhaps more importantly, men and women may also report symptoms differently, with women scoring higher on self-reported symptom intensity [32]. Somewhat surprisingly, symptom duration was not associated with CSI score.
Joint analysis of semicontinuous data with latent variables
2020, Computational Statistics and Data AnalysisCitation Excerpt :Recently, latent variables have also been introduced into the two-part model framework. Schneider and Stone (2014) proposed a two-part model with two latent outcomes where one was characterized by binary indicators of zero, another was characterized by observed positive continuous variables. Xia et al. (2019) investigated a two-part latent variable model with multivariate longitudinal data.