Differences In Intra-individual Variability Research Articles

A dynamic perspective on depressive symptoms during the first year postpartum.

The current study used novel methodology to characterize intraindividual variability in the experience of dynamic, within-person changes in postpartum depressive (PPD) symptoms across the first year postpartum and evaluated maternal and infant characteristics as predictors of between-person differences in intraindividual variability in PPD symptoms over time. With a sample of 322 low-income Mexican-origin mothers (Mage = 27.79; SD = 6.48), PPD symptoms were assessed at 11 time points from 3 weeks to 1 year postpartum (Edinburgh Perinatal Depression Scale; Cox & Holden, 2003). A prenatal cumulative risk index was calculated from individual psychosocial risk factors. Infant temperamental negativity was assessed via a maternal report at the infant age of 6 weeks (Infant Behavior Questionnaire; Putnam et al., 2014). Multilevel location scale analyses in a dynamic structural equation modeling (Asparouhov et al., 2018) framework were conducted. Covariates included prenatal depressive symptoms. On average, within-mother change in depressive symptoms at one time point was found to carry over to the next time point. Nonnull within-mother volatility in PPD symptoms reflected substantial ebbs and flows in PPD symptoms over the first year postpartum. Results of the between-level model demonstrated that mothers differed in their equilibriums, carryover, and volatility of their PPD symptoms. Mothers with more negative infants and those with higher prenatal cumulative risk exhibited higher equilibriums of PPD symptoms and more volatility in symptoms but did not differ in their carryover of PPD symptoms. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

5 Intraindividual Variability in Processing Speed on Digital Cognitive Assessments Differs by Amyloidosis Status in Cognitively Normal Older Adults

Objective:Intraindividual variability (IIV) is defined as fluctuations in an individual’s cognitive performance over time1. IIV has been identified as a marker of neurobiological disturbance making it a useful method for detecting changes in cognition among cognitively healthy individuals as well as those with prodromal syndromes2. IIV on laboratory-based computerized tasks has been linked with cognitive decline and conversion to mild cognitive impairment (MCI) and/or dementia (Haynes et al., 2017). Associations between IIV and AD risk factors including apolipoprotein (APOE) ε4 carrier status, neurodegeneration seen on brain imaging, and amyloid (Aß) Positron emission tomography (PET) scan status have also been observed1. Recent studies have demonstrated that evaluating IIV on smartphone-based digital cognitive assessments is feasible, has the capacity to differentiate between cognitively normal (CN) and MCI individuals, and may reduce barriers to cognitive assessment3. This study sought to evaluate whether such differences could be detected in CN participants with and without elevated AD risk.Participants and Methods:Participants (n=57) were cognitively normal older adults who previously received an Aß PET scan through the Butler Hospital Memory and Aging Program. The sample consisted of primarily non-Hispanic (n=49, 86.0%), White (n=52, 91.2%), college-educated (M=16.65 years), females (n=39, 68.4%). The average age of the sample was 68 years old. Approximately 42% of the sample (n=24) received a positive PET scan result. Participants completed brief cognitive assessments (i.e., 3-4 minutes) three times per day for eight days (i.e., 24 sessions) using the Mobile Monitoring of Cognitive Change (M2C2) application, a mobile app-based cognitive testing platform developed as part of the National Institute of Aging’s Mobile Toolbox initiative (Sliwinski et al., 2018). Participants completed visual working memory, processing speed, and episodic memory tasks on the M2C2 platform. Intraindividual standard deviations (ISDs) across trials were computed for each person at each time point (Hultsch et al., 2000). Higher ISD values indicate more variability in performance. Linear mixed effects models were utilized to examine whether differences in IIV existed based on PET scan status while controlling for age, sex at birth, and years of education.Results:n interaction between PET status and time was observed on the processing speed task such that Aß- individuals were less variable over the eight assessment days compared to Aß + individuals (B= -5.79, SE=2.67, p=.04). No main or interaction effects were observed on the visual working memory task or episodic memory task.Conclusions:Our finding that Aß- individuals demonstrate less variability over time on a measure of processing speed is consistent with prior work. No associations were found between IIV in other cognitive domains and PET status. As noted by Allaire and Marsiske (2005), IIV is not a consistent phenomenon across different cognitive domains. Therefore, identifying which tests are the most sensitive to early change is crucial. Additional studies in larger, more diverse samples are needed prior to widespread clinical use for early detection of AD.

Time-specific convergence and divergence in individual differences in behavior: Theory, protocols and analyzes.

Over the years, theoreticians and empiricists working in a wide range of disciplines, including physiology, ethology, psychology, and behavioral ecology, have suggested a variety of reasons why individual differences in behavior might change over time, such that different individuals become more similar (convergence) or less similar (divergence) to one another. Virtually none of these investigators have suggested that convergence or divergence will continue forever, instead proposing that these patterns will be restricted to particular periods over the course of a longer study. However, to date, few empiricists have documented time-specific convergence or divergence, in part because the experimental designs and statistical methods suitable for describing these patterns are not widely known. Here, we begin by reviewing an array of influential hypotheses that predict convergence or divergence in individual differences over timescales ranging from minutes to years, and that suggest how and why such patterns are likely to change over time (e.g., divergence followed by maintenance). Then, we describe experimental designs and statistical methods that can be used to determine if (and when) individual differences converged, diverged, or were maintained at the same level at specific periods during a longitudinal study. Finally, we describe why the concepts described herein help explain the discrepancy between what theoreticians and empiricists mean when they describe the "emergence" of individual differences or personality, how they might be used to study situations in which convergence and divergence patterns alternate over time, and how they might be used to study time-specific changes in other attributes of behavior, including individual differences in intraindividual variability (predictability), or genotypic differences in behavior.

Effects of Play in an Upright Position on Intra-Individual Variability of Gross Motor and Language Development in Institutionalized Infants.

(1) Objective: To investigate the effects of play in an upright position on intra-individual variability and to examine the relationship between the variability of gross motor and language development in institutionalized infants aged six to ten months. (2) Methods: Thirty infants were conveniently enrolled in either the experimental or control groups. The Alberta Infant Motor Scale (AIMS) and the Communication and Symbolic Behavior Scales Developmental Profile (CSBS-DP) Infant/Toddler Checklist were tested pre and post each monthly intervention for three months. Sixteen infants in the experimental group received an additional program of 45 min play in an upright position three times a week for a 3-month period. (3) Results: There were significant between-group differences in intra-individual variability of the AIMS percentiles (p-value = 0.042). In addition, there was a significant difference in the intra-individual variability of the language percentile between groups (p-value = 0.009). The intra-individual variability of gross motor development was significantly correlated (rs = 0.541; p = 0.03) with language development. (4) Conclusions: Play in an upright position could be applied to improve intra-individual variability in gross motor and language development percentiles in institutionalized infants.

Understanding the Error in Psychopathology: Notable Intraindividual Differences in Neural Variability of Performance Monitoring

BackgroundAbnormal performance monitoring is a possible transdiagnostic marker of psychopathology. Research on neural indices of performance monitoring, including the error-related negativity (ERN), typically examines group and interindividual (between-person) differences in mean/average scores. Intraindividual (within-person) variability in activity captures the capacity to dynamically adjust from moment to moment, and excessive variability appears maladaptive. Intraindividual variability in ERN represents a unique and largely unexamined dimension that might impact functioning. We tested whether psychopathology group differences (major depressive disorder, generalized anxiety disorder, obsessive-compulsive disorder) or corresponding psychiatric symptoms account for intraindividual variability in single-trial ERN scores. MethodsHigh-density electroencephalogram was recorded during a semantic flanker task in 51 participants with major depressive disorder, 44 participants with generalized anxiety disorder, 31 participants with obsessive-compulsive disorder, and 56 psychiatrically healthy participants. Time-window mean ERN amplitude was scored 0–125 ms following participant response across four frontocentral sites. Multilevel location-scale models were used to simultaneously examine interindividual and intraindividual differences in ERN. ResultsAnalyses indicated considerable intraindividual variability in ERN that was common across groups. However, we did not find strong evidence to support relationships between ERN and psychopathology groups or transdiagnostic symptoms. ConclusionsThese findings point to important methodological implications for studies of performance monitoring in healthy and clinical populations—the common assumption of fixed intraindividual variability (i.e., residual variance) may be inappropriate for ERN studies. Implementation of multilevel location-scale models in future research can leverage between-person differences in intraindividual variability in performance monitoring to gain a rich understanding of trial-to-trial performance monitoring dynamics.

Inter-individual differences in intra-individual variability in personality within and across contexts

This study focuses on intra-individual variability in personality at work, and how it relates to job performance. 288 professionals completed contextualised adjective-based personality assessments in work and non-work contexts, and a non-contextualised personality measure. Ratings of their personality were also obtained from colleagues, family members and friends. Supervisors provided performance ratings for 130 participants. Results indicate that personality is context- and source-dependent, and varies systematically within contexts intra-individually regardless of source. Whilst this variability was predictive of some performance criteria when based on other-ratings, overall predictive effects were small in number and size. This study adds to the relatively small body of research on personality variability and performance and contributes to the conceptualisation of personality as a dynamic construct.

Intra-Individual Variability in the Emergence of Complexity, Accuracy and Fluency in Speaking English at Secondary School: A Case Study of a Good, Average and Poor Language Learner

According to Complex Dynamic Systems Theory CDST, language is a complex dynamic system consisting of subsystems which show a lot of variability, especially during intensive development. Second language development is generally connected with an increase in complexity, accuracy and fluency but there are trade-offs within and between these language subcomponents. What is more, intra-individual variability, defined as differences in the level of developmental variables within individuals and between repeated measurements, is said to be an important developmental phenomenon. The aim of this article is to analyze the relationships between different measures of syntactic complexity, lexical complexity, accuracy and fluency, and to examine intra-individual variability with respect to the rate of development in longitudinal oral data provided by a good, average and poor language learner at the level of secondary school. Generally, the results of the study show some statistically significant differences between the learners in the development of these language subsystems but no such differences in intra-individual variability. Nevertheless, the study indicates a strong, positive correlation between the learners’ level of intra-individual variability and the rate of development of the language subsystems in speech at this level.

Thermal Perceptual Thresholds are typical in Autism Spectrum Disorder but Strongly Related to Intra-individual Response Variability

Individuals with autism spectrum disorder (ASD) are often reported to exhibit an apparent indifference to pain or temperature. Leading models suggest that this behavior is the result of elevated perceptual thresholds for thermal stimuli, but data to support these assertions are inconclusive. An alternative proposal suggests that the sensory features of ASD arise from increased intra-individual perceptual variability. In this study, we measured method-of-limits warm and cool detection thresholds in 142 individuals (83 with ASD, 59 with typical development [TD], aged 7–54 years), testing relationships with diagnostic group, demographics, and clinical measures. We also investigated the relationship between detection thresholds and a novel measure of intra-individual (trial-to-trial) threshold variability, a putative index of “perceptual noise.” This investigation found no differences in thermal detection thresholds between individuals with ASD and typical controls, despite large differences between groups in sensory reactivity questionnaires and modest group differences in intra-individual variability. Lower performance IQ, male sex, and higher intra-individual variability in threshold estimates were the most significant predictors of elevated detection thresholds. Although no psychophysical measure was significantly correlated with questionnaire measures of sensory hyporeactivity, large intra-individual variability may partially explain the elevated psychophysical thresholds seen in a subset of the ASD population.

The Power to Detect and Predict Individual Differences in Intra-Individual Variability Using the Mixed-Effects Location-Scale Model

ABSTRACTOur goal is to provide empirical scientists with practical tools and advice with which to test hypotheses related to individual differences in intra-individual variability using the mixed-effects location-scale model. To that end, we evaluate Type I error rates and power to detect and predict individual differences in intra-individual variability using this model and provide empirically-based guidelines for building scale models that include random and/or systematically-varying fixed effects. We also provide two power simulation programs that allow researchers to conduct a priori empirical power analyses. Our results aligned with statistical power theory, in that, greater power was observed for designs with more individuals, more repeated occasions, greater proportions of variance available to be explained, and larger effect sizes. In addition, our results indicated that Type I error rates were acceptable in situations when individual differences in intra-individual variability were not initially detectable as well as when the scale-model individual-level predictor explained all initially detectable individual differences in intra-individual variability. We conclude our paper by providing study design and model building advice for those interested in using the mixed-effects location-scale model in practice.

Intra-Individual Variability from a Lifespan Perspective: A Comparison of Latency and Accuracy Measures.

Within-task variability across trials (intra-individual variability (IIV)) has been mainly studied using latency measures but rarely with accuracy measures. The aim of the Geneva Variability Study was to examine IIV in both latency and accuracy measures of cognitive performance across the lifespan, administering the same tasks to children, younger adults, and older adults. Six processing speed tasks (Response Time (RT) tasks, 8 conditions) and two working memory tasks scored in terms of the number of correct responses (Working Memory (WM)—verbal and visuo-spatial, 6 conditions), as well as control tasks, were administered to over 500 individuals distributed across the three age periods. The main questions were whether age differences in IIV would vary throughout the lifespan according (i) to the type of measure used (RTs vs. accuracy); and (ii) to task complexity. The objective of this paper was to present the general experimental design and to provide an essentially descriptive picture of the results. For all experimental tasks, IIV was estimated using intra-individual standard deviation (iSDr), controlling for the individual level (mean) of performance and for potential practice effects. As concerns RTs, and in conformity with a majority of the literature, younger adults were less variable than both children and older adults, and the young children were often the most variable. In contrast, IIV in the WM accuracy scores pointed to different age trends—age effects were either not observed or, when found, they indicated that younger adults were the more variable group. Overall, the findings suggest that IIV provides complementary information to that based on a mean performance, and that the relation of IIV to cognitive development depends on the type of measure used.

Neurophysiological variability masks differences in functional neuroanatomical networks and their effectiveness to modulate response inhibition between children and adults.

Executive functions are well-known to undergo developmental changes from childhood to adulthood. Considerable efforts have been made to elucidate the affected system neurophysiological mechanisms. But while it is well-known that developmental changes affect intra-individual variability, this potential bias has largely been neglected when investigating the neurophysiology underlying developmental differences between children and adults. We hypothesize that due to differences in intra-individual variability of neural processes between children and adults, reliable group differences will only be evident after accounting for intra-individual variability in neurophysiological processes. We, therefore, investigate response-inhibition processes as an important instance of executive control in children (between 10 and 14years) and adults (between 20 and 29years) and decompose EEG data on the basis of the latency and temporal variability. This was combined with source localization. Children showed more impulsive behavior than adults. Importantly, a reliable match between the neurophysiological and behavioral data could only be found when accounting for intra-individual variability in the EEG data. These decomposed data showed that children and adults use similar neurophysiological mechanisms at the response selection level to accomplish inhibitory control, but seem to engage different neuroanatomical structures to do so according to source localization results: In adults, these processes were related to the medial frontal cortex. In children, the same processes were reflected in a shift of the scalp topography and related to the superior parietal cortex. These shifts in neural networks were associated with lower effectiveness in exerting inhibitory control. However, these differences in the functional neuroanatomical architecture can only be seen when intra-individual variability is taken into account.

Age and sex differences in intra-individual variability in a simple reaction time task

While age effects in reaction time (RT) tasks across the lifespan are well established for level of performance, analogous findings have started appearing also for indicators of intra-individual variability (IIV). Children are not only slower, but also display more variability than younger adults in RT. Yet, little is known about potential moderating sex effects on RT-IIV. We analyzed responses in a simple RT task with 120 trials in children, younger, and older adults. To best capture sex differences we used generalized additive models (GAMs), a semi-parametric regression approach, to fit splines relating nonlinearly age to RT, and capable of testing sex differences therein. This method is more adequate to test sex differences in nonlinear age relations than polynomial regression. Results show that (a) males are faster than females (except in the older adults), and (b) in younger and older adults, males are less variable than females. No sex difference in IIV emerged in children. Results are consistent with the hypothesis that sex differences in RT variability may be attributable to brain effects of sex hormones, in particular estrogen, whose receptors are present in several brain regions involved in information processing and attention, which are systems involved in the regulation of variability in information processing. Thus, according to this hypothesis, sex differences in RT-IIV should be present after puberty, but not in pre-pubertal children.

Pretreatment Differences in Intraindividual Variability in Reaction Time between Women Diagnosed with Breast Cancer and Healthy Controls.

Chemotherapy has adverse effects on cognitive performance in women treated for breast cancer, but less is known about the period before chemotherapy. Studies have focused on mean level of performance, yet there is increasing recognition that variability in performance within an individual is also an important behavioral indicator of cognitive functioning and underlying neural integrity. We examined intraindividual variability (IIV) before chemotherapy and surgery in women diagnosed with breast cancer (n=31), and a healthy control group matched on age and education (n=25). IIV was calculated across trials of a computerized Stroop task, including an examination of the slowest and fastest trials of reaction time (RT) responses. The groups were equivalent on overall accuracy and speed, and participants in both groups were less accurate and slower on incongruent trials compared with congruent trials. However, women with breast cancer became more variable with increased task difficulty relative to healthy controls. Among the slowest RT responses, women with breast cancer were significantly more variable than healthy controls on incongruent trials. This suggests that a specific variability-producing process (e.g., attentional lapses) occurs in task conditions that require executive control (e.g., incongruent trials). Results are consistent with other evidence of executive dysfunction among women treated for breast cancer. These findings highlight the importance of pretreatment assessment and show that variability in performance provides information about cognition that measures of central tendency do not.

The Power to Detect and Predict Individual Differences in Within-Person Variability Using the Mixed-Effects Location-Scale Model

Our goal is to provide empirical scientists with practical tools and advice with which to test hypotheses related to individual differences in intra-individual variability using the mixed-effects location-scale model. To that end, we evaluate Type I error rates and power to detect and predict individual differences in intra-individual variability using this model and provide empirically-based guidelines for building scale models that include random and/or systematically-varying fixed effects. We also provide two power simulation programs that allow researchers to conduct a priori empirical power analyses. Our results aligned with statistical power theory, in that, greater power was observed for designs with more individuals, more repeated occasions, greater proportions of variance available to be explained, and larger effect sizes. In addition, our results indicated that Type I error rates were acceptable in situations when individual differences in intra-individual variability were not initially detectable as well as when the scale-model individual-level predictor explained all initially detectable individual differences in intra-individual variability. We conclude our paper by providing study design and model building advice for those interested in using the mixed-effects location-scale model in practice.

Inter-limb coordination and control in boys with and without DCD in ball catching

The purpose of the study was to examine the nature of inter-limb coordination and control, exhibited by ten boys with (M=10.5years, SD=1.0) and without Developmental Coordination Disorder (DCD), in a ball catching task across different ball speeds. In line with the predictions of coordinated structure theory boys who were typically developing preserved strong and effective temporal relations when catching balls in baseline and fast conditions. Boys with DCD exhibited temporal symmetry in baseline but not in fast attempts, where the decoupling was uniformed across the group, coinciding with failures on ≥50% of the attempts. In terms of stability, no differences in intra-individual variability were observed between the groups. The analysis of spatial and temporal adaptations showed that boys who were typically developing, in essence, covered the same “ground” by decreasing their movement time. The opposite was true for boys with DCD who contacted the ball closer to the body, while failing to adapt the velocity of their hands. Taken together, both groups exhibited strong and stable coordinative relations, in a steady-state but not in a fast condition, where all boys with DCD failed to preserve the desired symmetry. This decoupling also coincided with different and less effective spatio-temporal adaptations at the effector level. Thus, it appears that movement control, hence flexibility of their synergistic relations, represents a movement limiter for boys with DCD who exhibit specific balls skills issues, at inter-limb level of organization. It should be noted, however, that large intra-group variance observed across some variables warrants caution when interpreting the aggregate data.

Stability of intraindividual variability as a marker of neurologic dysfunction in relapsing remitting multiple sclerosis

Background: Impairments in information processing speed are common in multiple sclerosis (MS), with affected individuals demonstrating slower responses and more intraindividual variability (IIV) in their performance on timed tasks. Evidence suggesting that IIV provides novel information about cognitive deficits in MS is accumulating; however, little is known about the stability of IIV across multiple assessments. In this study, we investigated IIV in response speed in persons with MS across 6 monthly sessions using the Attention Network Test–Interaction (ANT-I). Method: Individuals with relatively mild relapsing remitting MS and healthy controls completed the ANT-I at 6 monthly intervals. Clinical assessments (Sessions 1 and 6) and conventional magnetic resonance imaging (MRI) studies (Sessions 1–6) were examined for individuals with MS. Results: The MS group’s clinical and neuroimaging measures were stable during the 6-month period. Individuals with MS were slower and more variable in reaction time performance on the ANT-I than were controls. Differences in IIV between groups were maintained across the 6 sessions, with IIV demonstrating less susceptibility to across-session practice effects than mean latency scores. Conclusions: IIV provides a stable measure of cognitive performance in mildly affected persons with MS who are clinically and radiologically stable. Further studies exploring its utility as a clinical outcome are warranted.

Intraindividual variability is a fundamental phenomenon of aging: Evidence from an 8-year longitudinal study across young, middle, and older adulthood.

Moment-to-moment intraindividual variability (IIV) in cognitive speed is a sensitive behavioral indicator of the integrity of the aging brain and brain damage, but little information is known about how IIV changes from being relatively low in young adulthood to substantially higher in older adulthood. We evaluated possible age group, sex, and task differences in IIV across adulthood using a large, neurologically normal, population-based sample evaluated thrice over 8 years. Multilevel modeling controlling for education, diabetes, hypertension, and anxiety and depressive symptoms showed expected age group differences in baseline IIV across the adult lifespan. Increase in IIV was not found until older adulthood on simple tasks but was apparent even in the 40s on a more complex task. Females were more variable than males but only at baseline. IIV in cognitive speed is a fundamental behavioral characteristic associated with growing older, even among healthy adults.

Variety is the Spice of Life: A Microlongitudinal Study Examining Age Differences in Intraindividual Variability in Daily Activities in Relation to Sleep Outcomes

The relative importance of mean timing of daily activities versus intraindividual variability in the timing of daily activities in relation to health outcomes such as sleep has yet to be established. Furthermore, age-related changes in sleep could affect this relationship. The study objective was to examine the extent that intraindividual variability in the timing of daily activities is associated with sleep outcomes in younger and older adults. A microlongitudinal observational study design was used with 14 consecutive days of diaries in community-dwelling younger and older adults. 50 younger and 50 older adults completed daily assessments of activities and sleep. Three activities (going outside, starting work, and eating dinner) and 5 sleep (sleep onset latency, wake time after sleep onset, number of awakenings, total sleep time, and sleep quality rating) variables were used in the analyses. Hierarchical regressions revealed variability in the timing of daily activities significantly predicted sleep, beyond mean timing of activities, for 4 of 6 models. Results differed depending on the type of activity and age group. Intraindividual variability, not mean timing of daily activities, best-predicted sleep outcomes. Variability was associated with positive sleep outcomes for older, but not younger adults.

"Health is health is health? Age differences in intraindividual variability and in within-person versus between-person factor structures of self-reported health complaints": Correction to Wolff et al. (2012).

"Health is health is health? Age differences in intraindividual variability and in within-person versus between-person factor structures of self-reported health complaints": Correction to Wolff et al. (2012).

Health is health is health? Age differences in intraindividual variability and in within-person versus between-person factor structures of self-reported health complaints.

The variability of health complaints within individuals across time has rarely been studied, and the question whether between- and within-person factor structures of health-related variables are equivalent has not been tested so far. We examined self-reported health complaints in 101 younger (20-31 years) and 103 older adults (65-80 years) over a period of 100 daily assessments. Data were analyzed with confirmatory two-level factor analysis. One-factor structures of health complaints provided an acceptable fit at the between- and average within-person levels in both age groups, supporting the assumption of equivalent average within- and between-person factor structures for health complaints. Age differences in loading patterns indicated that subjective health may be experienced differently by younger and older adults. Small age differences in mean levels of health symptoms were observed. Intraindividual variability in health complaints was reliable. Older adults fluctuated less from day to day than younger adults, presumably reflecting less fluctuation in objective health, differences in response styles, situational influences, or habituation processes. We conclude that future research should consider intraindividual variability as being descriptive of a person's health status, and take possible differences between within- and between-person factor structures of subjective health into account.