Distinguishing between-person and within-person relationships in longitudinal health research: arthritis and quality of life

Checking Behavior, Fear of Recurrence, and Daily Triggers in Breast Cancer Survivors

BACKGROUND

Fear of cancer recurrence (FCR) is a top ongoing concern of breast cancer (BC) survivors and thus the focus of recent intervention development. The Self-Regulation Model of FCR (Lee-Jones C, Humphris G, Dixon R, Hatcher MB. Fear of cancer recurrence-a literature review and proposed cognitive formulation to explain exacerbation of recurrence fears. Psychooncology. 1997;6:95-105.) states that everyday cancer-related events trigger FCR, which, in turn, leads to specific behavioral responses, including checking the body for signs or symptoms of cancer. Links between triggering events, FCR, and checking behavior have not yet been studied in the context of daily life or at the within-person level.

PURPOSE

The goal of this study was to examine whether FCR has a within-person link with daily checking behavior and whether FCR mediates the link between triggering events and checking behavior.

METHODS

Seventy-two early-stage BC survivors completed daily diaries over a 21-day period approximately 5 months after BC surgery. FCR, checking behavior, and triggering events were assessed each evening.

RESULTS

Multilevel modeling results indicated that FCR predicted greater odds of same-day, but not next-day, checking behavior. We found that daily FCR significantly mediated the same-day effect of triggering events on checking behavior. These average within-person effects varied substantially between patients and were not explained by momentary negative affect.

CONCLUSIONS

Findings support the within-person relationship between triggering events, FCR, and checking behavior posited by guiding theory, and can inform FCR intervention development.

Between the Error Bars: How Modern Theory, Design, and Methodology Enrich the Personality-Health Tradition

The study of relationships between personality traits and health has a long history in psychosomatic research. However, personality science has evolved from an understanding of personality as fixed traits to one that acknowledges that personality is dynamic. Dynamic approaches to conceptualizing and measuring personality and individual differences can enrich personality-health research. In this Presidential Address (American Psychosomatic Society, 2018), I consider how different formulations of personality-stable traits, stable signals in a noisy or variable measure, within-person changes, and intraindividual variability-can be implemented to better understand how personality is related to health and particularly to immune function. These approaches recognize and, in some cases, capitalize on the fact that personality factors can display variability as well as stability over time. They also require repeated measurement and therefore greater methodological sophistication that considers reliability and generalizability, Simpson's paradox, and the difference between variability and flexibility. Dynamic qualities of personality and individual differences potentially influence health, and designs and methodology that incorporate them can illuminate the important processes that occur inside the error bars.

Calidad de vida, nivel de salud percibido y factores sociodemográficos en personas con artritis reumatoide

Objetivo: determinar la relación entre la calidad de vida, el nivel de salud y los factores sociodemográficos en personas con artritis reumatoide (AR). Materiales y método: estudio correlacional explicativo. Se realizó una entrevista directa en el momento de la consulta de enfermería antes del control médico de reumatología. A través de un muestreo intencional no probabilístico de sujetos tipo se contó con la participación de 635 personas. Resultados: se encontró una frecuencia de presentación de AR mayor en mujeres (87%). También se evidenció una correlación positiva (0,596; P<0,001) entre calidad de vida y nivel de salud. Sociodemográficamente, las mujeres con educación básica y bajo estrato socioeconómico presentan una menor percepción de calidad de vida y nivel de salud. Estas variables se sometieron a un proceso de prueba con el uso de un modelo Path de análisis de covarianza. Conclusiones: las condiciones sociales que viven las personas con AR son factores que determinan la puesta en marcha de acciones de intervención dirigidas a solucionar la problemática de la calidad de vida en esta población.

Self-rated health and interleukin-6: Longitudinal relationships in older adults

BACKGROUND

Both self-rated health (SRH) and inflammation are implicated in chronic diseases and premature mortality. Better SRH is associated with lower proinflammatory cytokines, but there is little evidence about whether this relationship is more stable or dynamic.

OBJECTIVE

To study the between- and within-person associations between SRH and IL-6.

METHODS

Older adults (N=131; Mage=75 years) rated their health and provided blood samples for analysis of IL-6 at separate occasions every 6 months over a period up to 5 years. Age, sex, BMI, neuroticism, and statin use were examined as covariates in multilevel models.

RESULTS

In bivariate models, better SRH, lower BMI, younger age, and female sex correlated with lower IL-6. In multilevel models, stable SRH (between-person differences; p<.001) but not dynamic SRH (within-person changes; p=.93) correlated with IL-6. The stable relationship persisted with demographic and health covariates in the model.

CONCLUSIONS

Better stable SRH but not dynamic SRH was robustly associated with lower IL-6 among older adults, lending support to previous cross-sectional findings on the relation between inflammatory markers and SRH. The findings suggest that trait-like mechanisms, rather than changes over a time scale of 6-month waves, govern this association. To further investigate the mechanisms behind the SRH-IL-6 association, studies with different measurement frequencies, higher within-person variability, and experimental approaches are warranted.

Weekly Cycles in Daily Report Data: An Overlooked Issue

Daily diaries and other everyday experience methods are increasingly used to study relationships between two time-varying variables X and Y. Although daily data potentially often have weekly cyclical patterns (e.g., stress may be higher on weekdays and lower on weekends), the majority of daily diary studies have ignored this possibility. In this study, we investigated the effect of ignoring existing weekly cycles. We reanalyzed an empirical dataset (stress and alcohol consumption) and performed Monte Carlo simulations to investigate the impact of omitting weekly cycles. In the empirical dataset, ignoring cycles led to the inference of a significant within-person X-Y relation whereas modeling cycles suggested that this relationship did not exist. Simulation results indicated that ignoring cycles that existed in both X and Y led to bias in the estimated within-person X-Y relationship. The amount and direction of bias depended on the magnitude of the cycles, magnitude of the true within-person X-Y relation, and synchronization of the cycles. We encourage researchers conducting daily diary studies to address potential weekly cycles in their data. We provide guidelines for detecting and modeling cycles to remove their influence and discuss challenges of causal inference in daily experience studies.

Affect and self-rated health: a dynamic approach with older adults

OBJECTIVE

Self-rated health (SRH) predicts mortality above and beyond objective health risks and, as such, comprises an important aspect of health. Established contributors to SRH include affect, age, and disease, but neither their dynamic nor their synergistic contributions to SRH have been comprehensively tested.

METHOD

The present study employed older adults (N = 150; Mage = 75 years) and a longitudinal design with 6-month waves over a period up to 5 years. Positive (PA) and negative affect (NA), chronic disease, and SRH were assessed at each wave.

RESULTS

In multilevel models with single predictors, older age, more chronic disease, and higher NA predicted worse SRH, whereas higher PA predicted better SRH. Affect predicted SRH both between and within people. In multilevel models with interactions between affect and age or disease, individual differences in NA predicted worse SRH primarily in older people. Within people, changes in NA were associated with changes in SRH, but more so in younger than in older people. Within people, changes in PA were associated with changes in SRH, but only when health was better than usual.

CONCLUSION

There were both dynamic and synergistic relationships between affect and SRH that could only emerge in a multilevel, multivariable design. In the case of NA, between-person, trait NA had the opposite relationship to SRH and age compared to within-person, state NA. Which component of this relationship predicts mortality is an important question for future research.