Daily Diary Data Research Articles

BFF: Bayesian, Fiducial, Frequentist Analysis of Age Effects in Daily Diary Data.

We apply new statistical models to daily diary data to advance both methodological and conceptual goals. We examine age effects in within-person slopes in daily diary data and introduce Generalized Fiducial Inference (GFI), which provides a compromise between frequentist and Bayesian inference. We use daily stressor exposure data across six domains to generate within-person emotional reactivity slopes with daily negative affect. We test for systematic age differences and similarities in these reactivity slopes, which are inconsistent in previous research. One hundred and eleven older (aged 60-90) and 108 younger (aged 18-36) adults responded to daily stressor and negative affect questions each day for eight consecutive days, resulting in 1,438 total days. Daily stressor domains included arguments, avoided arguments, work/volunteer stressors, home stressors, network stressors, and health-related stressors. Using Bayesian, GFI, and frequentist paradigms, we compared results for the six stressor domains with a focus on interpreting age effects in within-person reactivity. Multilevel models suggested null age effects in emotional reactivity across each of the paradigms within the domains of avoided arguments, work/volunteer stressors, home stressors, and health-related stressors. However, the models diverged with respect to null age effects in emotional reactivity to arguments and network stressors. The three paradigms converged on null age effects in reactivity for four of the six stressor domains. GFI is a useful tool that provides additional information when making determinations regarding null age effects in within-person slopes. We provide the code for readers to apply these models to their own data.

Personal resource profiles of individuals with chronic pain: Sociodemographic and pain interference differences.

Previous studies have demonstrated important associations between personal resources and pain interference. Using latent profile analysis, the present study (a) identified subgroups of individuals with chronic pain who have different personal resource profiles; (b) explored sociodemographic differences among subgroups; and (c) examined how these subgroups differ in pain interference. Research Method/Design: Study 1 is based on daily diary and survey data from 220 individuals with fibromyalgia (FM). Study 2 is based on 4 annual surveys of 483 individuals with long-term neurological/neuromuscular disease or injury, and chronic pain. Modifiable personal resource variables including sense of resilience, social support, pain acceptance, and sleep quality were included in latent profile analyses. Three subgroups were identified in both studies: High, Moderate, and Low Personal Resource groups. In both studies, annual income level was significantly different among subgroups. Study 1 results showed a significant between-groups difference in pain interference across 21-days only between High and Moderate Personal Resource groups controlling for the level of pain intensity and depressive symptoms. In Study 2, however, all subgroups were significantly different with respect to their levels of pain interference at baseline over and above various covariates, with the Low Personal Resource group reporting the highest level of pain interference at baseline. These baseline differences remained stable over 4 years. The findings suggest a robust association between economic disparity and personal resource profiles among individuals with chronic pain. The role of different personal resource profiles in pain interference appears to differ by chronic pain condition. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Stress-Buffering Effects of Volunteering on Daily Well-Being: Evidence From the National Study of Daily Experiences.

Building on theoretical frameworks and empirical evidence linking volunteering and well-being in later life, we investigated the associations between daily engagement in formal volunteering, stressors, and negative and positive affect, focusing on the stress-buffering effect of volunteering. We used 8 days of daily diary data from the second wave of the National Study of Daily Experiences (NSDE II), a national survey of middle-aged and older adults (participant N = 1,320; participant-day observation N = 8,277). A series of multilevel models were estimated to assess the within-person associations between daily volunteering, stressors, and affect. A direct link between daily volunteering and affect was not discovered. However, we found that the association between daily stressors and negative affect (but not positive affect) was weaker on days when volunteering was performed compared to days volunteering was not performed. Our findings suggested that the stress-buffering effect of volunteering contributes to improved emotional well-being for participants who volunteered on a daily basis. Future studies should investigate whether such stress-buffering effects are present for other forms of helping behaviors.

Daily technology interruptions and emotional and relational well-being

The current abundance of technology in daily life creates opportunities for interruptions in couple interactions, termed technoference or phubbing. The current study examined reports from both partners in 173 romantic relationships who completed daily surveys on technoference and relational well-being measures across 14 days. By using daily diary data, we were able to examine within-person associations and more closely approximate everyday life. Utilizing multilevel modeling, we found that on days when participants rated more technoference than usual, they felt worse about their relationship, perceived more conflict over technology use, rated their face-to-face interactions as less positive, and experienced more negative mood. These relationships existed even after controlling for general feelings of relationship dissatisfaction, depression, and attachment anxiety, and there were no significant differences between women and men in these associations. This suggests that regardless of an individual's or a couple's current level of well-being, if individuals perceive technology use as interfering in their interactions with their partner, these perceptions may affect their daily assessments of their relationship and mood.

A Novel Method for Analysing Frequent Observations from Questionnaires in Order to Model Patient-Reported Outcomes: Application to EXACT\xae Daily Diary Data from COPD Patients

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease with approximately 174 million cases worldwide. Electronic questionnaires are increasingly used for collecting patient-reported-outcome (PRO) data about disease symptoms. Our aim was to leverage PRO data, collected to record COPD disease symptoms, in a general modelling framework to enable interpretation of PRO observations in relation to disease progression and potential to predict exacerbations. The data were collected daily over a year, in a prospective, observational study. The e-questionnaire, the EXAcerbations of COPD Tool (EXACT®) included 14 items (i.e. questions) with 4 or 5 ordered categorical response options. An item response theory (IRT) model was used to relate the responses from each item to the underlying latent variable (which we refer to as disease severity), and on each item level, Markov models (MM) with 4 or 5 categories were applied to describe the dependence between consecutive observations. Minimal continuous time MMs were used and parameterised using ordinary differential equations. One hundred twenty-seven COPD patients were included (median age 67 years, 54% male, 39% current smokers), providing approximately 40,000 observations per EXACT® item. The final model suggested that, with time, patients more often reported the same scores as the previous day, i.e. the scores were more stable. The modelled COPD disease severity change over time varied markedly between subjects, but was small in the typical individual. This is the first IRT model with Markovian properties; our analysis proved them necessary for predicting symptom-defined exacerbations.

Exploring the promise of assessing dynamic characteristics of the family for predicting adolescent risk outcomes.

Family-based assessments of risk factors for adolescent emotional, behavioral, and substance use problems can be used to identify adolescents who are at risk and intervene before problems cause clinically significant impairment. Expanding traditional methods for assessing risk, this study evaluates whether lability, referring to the degree to which parent-adolescent relationships and parenting fluctuate from day to day, might offer additional value to assessment protocols aimed at identifying precursor risk factors. This study sampled 151 adolescents and caregivers, collecting data at a baseline assessment, a 21-day daily diary protocol, and a 12-month follow-up assessment. Daily diary data were used to calculate within-family lability scores in parenting practices, parent-adolescent connectedness, and parent-adolescent conflict. Regression analyses evaluated whether lability predicted adolescent's depression, anxiety, antisocial behavior (ASB), drunkenness, and marijuana use at 12-month follow-up. Lability in parent-adolescent connectedness, accounting for baseline levels, gender, age, and initial levels of outcomes, was associated with risk for depression, anxiety, ASB, drunkenness, and marijuana use. Lability in parenting practices also was associated with risk for depression, anxiety, and drunkenness. Baseline levels moderated some of these effects. Parent-adolescent conflict lability was only associated with depression. These findings provide evidence for substantial value added when including dynamic assessments of family lability in predicting long-term adolescent risk outcomes and call for integration of dynamic methods into assessment practices.

Do Family Relationships Buffer the Impact of Disability on Older Adults' Daily Mood? An Exploration of Gender and Marital Status Differences.

We evaluate whether non-spousal family support and strain moderate the effect of disability on two daily emotions (happiness and frustration) among older adults, and whether these patterns differ by gender among married persons, and by marital status among women. Stress buffering perspectives predict that harmful effects of stress on well-being are buffered by family support, whereas stress proliferation models suggest these effects are intensified by family strain. The extent to which family relationships moderate associations between stress and well-being may vary on the basis of gender and marital status, as non-spousal family ties are considered especially salient for women and those without a romantic partner. Daily diary data are from the 2013 Disability and Use of Time supplement to the Panel Study of Income Dynamics (n=1,474), a national sample of adults ages 60+. Multivariate regression models are estimated for married/partnered men and women, and formerly married women. Neither family support nor strain moderated the effect of severe impairment on married men's daily emotions. Family support buffered the effect of severe impairment on frustration among divorced and widowed women, but not their married counterparts. Counterintuitively, family arguments mitigated against frustration and increased happiness among married women with severe impairment. Consistent with stress buffering perspectives, family support was most protective for the vulnerable population of formerly married older women with severe impairment. This study underscores the importance of family support for the large and growing population of formerly married women managing health-related challenges in later life.

Uncovering general, shared, and unique temporal patterns in ambulatory assessment data.

Intensive longitudinal data provide psychological researchers with the potential to better understand individual-level temporal processes. While the collection of such data has become increasingly common, there are a comparatively small number of methods well-suited for analyzing these data, and many methods assume homogeneity across individuals. A recent development rooted in structural equation and vector autoregressive modeling, Subgrouping Group Iterative Multiple Model Estimation (S-GIMME), provides one method for arriving at individual-level models composed of processes shared by the sample, a subset of the sample, and a given individual. As this algorithm was motivated and validated for use with neuroimaging data, its performance is less understood in the context of ambulatory assessment data. Here, we evaluate the performance of the S-GIMME algorithm across various conditions frequently encountered with daily diary (compared to neuroimaging) data; namely, a smaller number of variables, a lower number of time points, and smaller autoregressive effects. We demonstrate, for the first time, the importance of the autoregressive effects in recovering data-generating connections and directions, and the ability to use S-GIMME with lengths of data commonly seen in daily diary studies. We demonstrate the use of S-GIMME with an empirical example evaluating the general, shared, and unique temporal processes associated with a sample of individuals with borderline personality disorder (BPD). Finally, we underscore the need for methods such as S-GIMME moving forward given the increasing use of intensive longitudinal data in psychological research, and the potential for these data to provide novel insights into human behavior and mental health. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

On Standardizing Within-Person Effects: Potential Problems of Global Standardization

Person-mean centering has been recommended for disaggregating between-person and within-person effects when modeling time-varying predictors. Multilevel modeling textbooks recommended global standardization for standardizing fixed effects. An aim of this study is to evaluate whether and when person-mean centering followed by global standardization can accurately estimate fixed-effects within-person relations (the estimand of interest in this study) in multilevel modeling. We analytically derived that global standardization generally yields inconsistent (asymptotically biased) estimates for the estimand when between-person differences in within-person standard deviations exist and the average within-person relation is nonzero. Alternatively, a person-mean-SD standardization (P-S) approach yields consistent estimates. Our simulation results further revealed (1) how misleading the results from global standardization were under various circumstances and (2) the P-S approach had accurate estimates and satisfactory coverage rates of fixed-effects within-person relations when the number of occasions is 30 or more (in many conditions, performance was satisfactory with 10 or 20 occasions). A daily diary data example, focused on emotional complexity, was used to empirically illustrate the approaches. Researchers should choose standardization approaches based on theoretical considerations and should clearly describe the purpose and procedure of standardization in research articles.

Time Series Visualizations of Mobile Phone-Based Daily Diary Reports of Stress, Physical Activity, and Diet Quality in Mostly Ethnic Minority Mothers: Feasibility Study.

BackgroundHealth behavior patterns reported through daily diary data are important to understand and intervene upon at the individual level in N-of-1 trials and related study designs. There is often interest in relationships between multiple outcomes, such as stress and health behavior. However, analyses often utilize regressions that evaluate aggregate effects across individuals, and standard analyses target single outcomes.ObjectiveThis paper aims to illustrate how individuals’ daily reports of stress and health behavior (time series) can be explored using visualization tools.MethodsSecondary analysis was conducted on 6 months of daily diary reports of stress and health behavior (physical activity and diet quality) from mostly ethnic minority mothers who pilot-tested a self-monitoring mobile health app. Time series with minimal missing data from 14 of the 44 mothers were analyzed. Correlations between stress and health behavior within each time series were reported as a preliminary step. Stress and health behavior time series patterns were visualized by plotting moving averages and time points where mean shifts in the data occurred (changepoints).ResultsMedian correlation was small and negative for associations of stress with physical activity (r=−.14) and diet quality (r=−.08). Moving averages and changepoints for stress and health behavior were aligned for some participants but not for others. A third subset of participants exhibited little variation in stress and health behavior reports.ConclusionsMedian correlations in this study corroborate prior findings. In addition, time series visualizations highlighted variations in stress and health behavior across individuals and time points, which are difficult to capture through correlations and regression-based summary measures.

STRESS-BUFFERING EFFECTS OF VOLUNTEERING ON SALIVARY CORTISOL: RESULTS FROM A DAILY DIARY STUDY

Abstract Based on the theoretical foundations of the caregiving system model, which holds that prosocial behavior can be conceptualized in relation to a neurobiological stress-buffering mechanism, we addressed the question of whether daily volunteering yields buffering effects in terms of suppressing a neuroendocrine response (i.e., salivary cortisol) to daily stressors. We used daily diary data from the second wave of the National Study of Daily Experiences (NSDE II), which is part of the Midlife in the United States study (MIDUS II), a nationally representative survey of middle-aged and older adults. Analyzing a sample of volunteers (N = 340), we tested the buffering role of daily volunteer work for the same day stressors-salivary cortisol response relationship (person-day observations, N = 1,042). Findings from multilevel models indicated that the relationship between daily stressors and cortisol output was attenuated on days when volunteering was performed compared to days volunteering was not performed. Our findings are suggestive of a unique, but unobserved, neurobiological mechanism underlying the link between volunteering and better health. Volunteer programs designed to help others in need may be considered as an intervention strategy for individuals living under stressful conditions.

Using spectral and cross-spectral analysis to identify patterns and synchrony in couples' sexual desire.

Sexual desire discrepancy is one of the most frequently reported sexual concerns for individuals and couples and has been shown to be negatively associated with sexual and relationship satisfaction. Sexual desire has increasingly been examined as a state-like construct that ebbs and flows, but little is known about whether there are patterns in the fluctuation of sexual desire. Utilizing spectral and cross-spectral analysis, we transformed 30 days of dyadic daily diary data for perceived levels of sexual desire for a non-clinical sample of 133 couples (266 individuals) into the frequency domain to identify shared periodic state fluctuations in sexual desire. Spectral analysis is a technique commonly used in physics and engineering that allows time series data to be analyzed for the presence of regular cycles of fluctuation. Cross-spectral analysis allows for dyadic data to be analyzed for shared rates of fluctuation between partners as well as the degree of (a)synchrony (or phase shift) between these fluctuations. Men and women were found to exhibit fluctuations in sexual desire at various frequencies including rates of once and twice per month, and to have sexual desire that was unlikely to fluctuate over periods of three days or less and therefore exhibited persistence. Similar patterns of fluctuation were exhibited within couples and these patterns were found to be largely synchronous. While instances of desire discrepancy may arise due to differences in rates of sexual desire fluctuation and random fluctuations, such instances may be normal for romantic relationships. The results have important implications for researchers, clinicians, and educators in that they corroborate the supposition that sexual desire ebbs and flows and suggest that it does so with predictable regularity.

A sorrow halved? A daily diary study on talking about experienced workplace incivility and next-morning negative affect.

Incivility by coworkers and customers can have detrimental consequences for employees' affective well-being at work. However, little is known about whether incivility also impairs employees' affect at home and how long these negative effects may last. In this diary study, we examine whether incivility by coworkers and customers is related to next-morning negative affect via negative affect at the end of the workday and at bedtime, and investigate different modes of social sharing (i.e., conversations about experienced mistreatment) as day-level moderators of this relationship. Daily diary data collected over 10 workdays (N = 113 employees) revealed that coworker incivility was indirectly related to bedtime negative affect via negative affect at the end of the workday, and customer incivility was indirectly related to next-morning negative affect via negative affect at the end of the workday and at bedtime. Although we found no moderating effect for conversations in an affective sharing mode (i.e., conversation partners provide comfort and consolation), the relationship between workplace incivility and employees' negative affect was buffered by conversations in a cognitive sharing mode (i.e., conversation partners suggest alternative explanations or reappraisal of uncivil behavior). In line with social sharing theory, our results suggest that talking about experienced mistreatment can, under specific circumstances, offset the negative relationship of uncivil coworker and customer behavior and employees' negative affect. This study advances current research on workplace incivility by studying negative affect 3 times a day and thus sheds light on the mechanism connecting workplace incivility and employees' affective well-being at home. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Does Working Memory Moderate the Within-Person Associations Between Pain Intensity and Negative Affect and Pain's Interference With Work Goal Pursuit?

Chronic pain exerts a pervasive negative influence on workers' productivity. However, a paucity of research has addressed the mechanisms underlying the pain → productivity relation. In the present study using intensive daily diary data, we examined whether working memory (WM) moderates the positive within-person associations between (1) morning pain intensity and (2) morning negative affect (NA) and later day pain's interference of work-goal (WG) pursuit. A community sample of 131 adults with chronic pain completed a battery of questionnaires, laboratory-measured WM, and a 21-day daily diary. WM did not moderate the positive within-person association between morning pain intensity and afternoon/evening ratings of pain's interference with work goal pursuit. However, individuals with higher WM showed significantly attenuated positive within-person association between morning negative affect and pain's interference with afternoon/evening work goal pursuit. WM appears to protect goal-relevant information from distractions due to negative affective arousal. The continued use of ecologically valid observational and intervention studies would shed further light on the influence of WM on the pursuit of valued work goals in the face of pain and negative affect.

Multilevel autoregressive mediation models: Specification, estimation, and applications.

In the current study, extending from the cross-lagged panel models (CLPMs) in Cole and Maxwell (2003), we proposed the multilevel autoregressive mediation models (MAMMs) by allowing the coefficients to differ across individuals. In addition, Level-2 covariates can be included to explain the interindividual differences of mediation effects. Given the complexity of the proposed models, Bayesian estimation was used. Both a CLPM and an unconditional MAMM were fitted to daily diary data. The 2 models yielded different statistical conclusions regarding the average mediation effect. A simulation study was conducted to examine the estimation accuracy of Bayesian estimation for MAMMs and consequences of model mis-specifications. Factors considered included the sample size (N), number of time points (T), fixed indirect and direct effect sizes, and Level-2 variances and covariances. Results indicated that the fixed effect estimates for the indirect effect components (a and b) and the fixed effects of Level-2 covariates were accurate when N ≥ 50 and T ≥ 5. For estimating Level-2 variances and covariances, they were accurate provided a sufficiently large N and T (e.g., N ≥ 500 and T ≥ 50). Estimates of the average mediation effect were generally accurate when N ≥ 100 and T ≥ 10, or N ≥ 50 and T ≥ 20. Furthermore, we found that when Level-2 variances were zero, MAMMs yielded valid inferences about the fixed effects, whereas when random effects existed, CLPMs had low coverage rates for fixed effects. DIC can be used for model selection. Limitations and future directions were discussed. (PsycINFO Database Record

25-Hydroxyvitamin D and Long Menstrual Cycles in a Prospective Cohort Study.

Vitamin D insufficiency is associated with subfertility and prolonged estrus cycles in animals, but humans have not been well studied. A prospective time-to-pregnancy study, Time to Conceive (2010-2015), collected up to 4 months of daily diary data. Participants were healthy, late reproductive-aged women in North Carolina who were attempting pregnancy. We examined menstrual cycle length as a continuous variable and in categories: long (35+ days) and short (≤25 days). Follicular phase length and luteal phase length were categorized as long (18+ days) or short (≤10 days). We estimated associations between those lengths and serum 25-hydroxyvitamin D (25[OH]D) using linear mixed models and marginal models. There were 1,278 menstrual cycles from 446 women of whom 5% were vitamin D deficient (25[OH]D, <20 ng/ml), 69% were between 20 and 39 ng/ml, and 26% were 40 ng/ml or higher. There was a dose-response association between vitamin D levels and cycle length. Compared with the highest 25(OH)D level (≥40 ng/ml), 25(OH)D deficiency was associated with almost three times the odds of long cycles (adjusted odds ratio [aOR] = 2.8 [95% confidence interval (CI) = 1.0, 7.5]). The aOR was 1.9 (1.1, 3.5) for 20 to <30 ng/ml. The probability of a long follicular phase and the probability of a short luteal phase both increased with decreasing 25(OH)D. Lower levels of 25(OH)D are associated with longer follicular phase and an overall longer menstrual cycle. Our results are consistent with other evidence supporting vitamin D's role in the reproductive axis, which may have broader implications for reproductive success.

A Daily Diary Investigation of the Link Between Television Watching and Positive Affect

Past research has shown a negative relationship between time spent watching television (TV) and several indicators of hedonic well-being—including positive affect (PA). However, cross-sectional designs employed in most of these studies do not allow for inferences regarding the direction of the link between TV watching and PA. Present research aimed to address this gap by using daily diary data from a large national sample of U.S. adults (N = 1668, age = 33–83 years). Respondents reported time spent watching TV as well as PA for eight consecutive days. Results of multilevel modeling analyses showed that duration of TV watching on the previous day did not significantly predict changes in PA on the next day. However, PA on the previous day significantly predicted decreases in duration of TV watching the following day. The results held after controlling for factors known to predict duration of TV watching and PA (i.e., age, gender, income level, employment status, marital status, health status, and personality traits). The present research goes beyond past cross-sectional work by shedding light on the direction of the link between TV watching and PA. Our findings indicate that watching TV does not seem to diminish PA—as critics of TV proclaim—but individuals seem to watch TV to a greater extent whenever they experience reduced PA.

Stress-buffering effects of volunteering on salivary cortisol: Results from a daily diary study

Based on the theoretical foundations of the caregiving system model, which holds that prosocial behavior can be conceptualized in relation to a neurobiological stress-buffering mechanism, we addressed the question of whether daily volunteering yields buffering effects in terms of suppressing a neuroendocrine response (i.e., salivary cortisol) to daily stressors. We used daily diary data from the second wave of the National Study of Daily Experiences (NSDE II), which is part of the Midlife in the United States study (MIDUS II), a nationally representative survey of middle-aged and older adults. Analyzing a sample of volunteers (N = 340), we tested the buffering role of daily volunteer work for the same day stressors-salivary cortisol response relationship (person-day observations, N = 1,042). Findings from multilevel models indicated that the relationship between daily stressors and cortisol output was attenuated on days when volunteering was performed compared to days volunteering was not performed. Our findings are suggestive of a unique, but unobserved, neurobiological mechanism underlying the link between volunteering and better health. Volunteer programs designed to help others in need may be considered as an intervention strategy for individuals living under stressful conditions.

Does alexithymia moderate the relation between stress and general sleep experiences?

A tendency for experiencing unusual dream and sleep-wake transition phenomena (e.g., recurrent dreams, hypnagogic hallucinations, and confusion upon awakening), labeled general sleep experiences (GSEs), is linked with stress as well as psychological distress, explicit as well as covert. We hypothesized that alexithymia may moderate the relationship between stress and GSEs. Undergraduate students (N=187) completed online questionnaires; Three months later, n=78 of them reported perceived stress and dreaming each day for 14days. Regression analyses for trait data and multilevel modeling for daily diary data both revealed a pattern of two competing alexithymic mechanisms: difficulty in identifying feelings was related to increased GSEs, whereas externally-oriented thinking was related to decreased GSEs. As hypothesized, a cross-level interaction was found: daily stress predicted daily GSEs of the following night, only among those who reported difficulty identifying their emotions. It seems that those who experience GSEs following stress, tend to be internally-oriented (i.e., notice their inner experiences), yet find it difficult to understand and identify those experiences. GSEs seem to represent a nocturnal manifestation of unprocessed emotion.

Validation of Sun Exposure Reported Annually Against Interim Self-report and Daily Sun Diaries.

Data on personal sun exposure over a period exceeding the immediate past days or weeks are typically self-reported in brief questionnaire items. The validity of such self-reporting of longer term personal sun exposure, for example over a year, including detail on variation across seasons, has not previously been investigated. In a volunteer sample (n=331) of Australian adults aged 18years and over, we assessed the 12-month reliability of sun exposure reported separately for each season, and its accuracy compared to a daily sun diary in the same season. Seasonal time outdoors displayed fair-to-good reliability between baseline and end of study (12months), with responses showing higher agreement at lower levels of time outdoors. There was good agreement for ranking of individuals' time outdoors with the daily sun diary data, although the actual diary time outdoors was typically considerably lower than the self-reported questionnaire data. Place of residence, education, being a smoker, day of the week (i.e. working day vs nonworking day) and working mainly outdoors were significant predictors of agreement. While participants overestimated their actual time outdoors, the self-report questionnaire provided a valid ranking of long-term sun exposure against others in the study that was reliable over time.