Evidence suggests that relations between child care and childrens development-behaviorally and physiologically-likely differ between children from high-versus low-risk contexts. Using data from the Family Life Project (N = 1,155), the authors tested (a) whether within- and between-child differences in childrens child care experiences (i.e., quantity, type, caregiver responsivity, and peer exposure) were predictive of their cortisol levels across infancy and toddlerhood and (b) whether these relations differed for children experiencing different levels of environmental risk. They found some evidence of such interactive effects. For children from high-risk contexts, within-child increases in child care hours were predictive of cortisol decreases. The inverse was evident for children from low-risk contexts. This relation grew across toddlerhood. Whereas a history of greater center-based child care was predictive of heightened cortisol levels for low-risk families, this was not the case for children from high-risk families. Irrespective of risk, greater peer exposure (between children) was associated with lower cortisol levels.

Evidence suggests that relations between child care and children's development-behaviorally and physiologically-likely differ between children from high-versus low-risk contexts. Using data from the Family Life Project (N = 1,155), the authors tested (a) whether within- and between-child differences in children's child care experiences (i.e., quantity, type, caregiver responsivity, and peer exposure) were predictive of their cortisol levels across infancy and toddlerhood and (b) whether these relations differed for children experiencing different levels of environmental risk. They found some evidence of such interactive effects. For children from high-risk contexts, within-child increases in child care hours were predictive of cortisol decreases. The inverse was evident for children from low-risk contexts. This relation grew across toddlerhood. Whereas a history of greater center-based child care was predictive of heightened cortisol levels for low-risk families, this was not the case for children from high-risk families. Irrespective of risk, greater peer exposure (between children) was associated with lower cortisol levels.

The relation of the cumulative experience of poverty in infancy and early childhood to child cortisol at age 48 months was examined in a prospective longitudinal sample of children and families (N=1292) in predominantly low-income and rural communities in two distinct regions of the United States. Families were seen in the home for data collection and cumulative experience of poverty was indexed by parent reported income-to-need ratio and household chaos measures collected between child ages 2 months and 48 months. For the analysis presented here, three saliva samples were also collected over an approximate 90 min interval at child age 48 months and were assayed for cortisol. ECG data were also collected during a resting period and during the administration of a mildly challenging battery of cognitive tasks. Mixed model analysis indicated that child cortisol at 48 months decreased significantly over the sampling time period and that cumulative time in poverty (number of years income-to-need less than or equal to 1) and cumulative household chaos were significantly related to a flatter trajectory for cortisol change and to an overall higher level of cortisol, respectively. Findings also indicated that respiratory sinus arrhythmia derived from the ECG data moderated the association between household chaos and child cortisol and that increase in respiratory sinus arrhythmia during the cognitive task was associated with an overall lower level of cortisol at 48 months.

This study evaluated continuity and change in maternal-child hypothalamic-pituitary-adrenal axis attunement in early childhood. Participants were drawn from a prospective study of 1,292 mother-child dyads, which were racially diverse, predominantly low-income, and non-urban. Child focused stress tasks designed to elicit anger, fear, and frustration were administered during early infancy, later infancy, and toddlerhood. Mothers and childrens saliva samples (later assayed for cortisol) were collected before and after the tasks. The strength of mother-child adrenocortical attunement was conserved across infancy and toddlerhood. The magnitude of maternal-child adrenocortical attunement decreased in response to the child-focused stress tasks. Maternal sensitivity and the childs task-related emotional reactivity moderated adrenocortical attunement across the task, with greater maternal sensitivity during a free-play, and lower levels of child emotional reactivity during the stress tasks, stabilizing attunement from pre- to post-task levels. The findings advance our understanding of individual differences in the social regulation of adrenocortical activity in early childhood.

Best practice standards for measuring analyte levels in saliva recommend that all biospecimens be tested in replicate with mean concentrations used in statistical analyses. This approach prioritizes minimizing laboratory-based measurement error but, in the process, expends considerable resources. We explore the possibility that, due to advances in salivary assay precision, the contribution of laboratory-based measurement error in salivary analyte data is very small relative to more important and meaningful variability in analyte levels across biological replicates (i.e., between different specimens). To evaluate this possibility, we examine the utility of the repeatability intra-class correlation (rICC) as an additional index of salivary analyte data precision. Using randomly selected subsamples (Ns=200 and 60) of salivary analyte data collected as part of a larger epidemiologic study, we compute the rICCs for seven commonly assayed salivary measures in biobehavioral research - cortisol, alpha-amylase, c-reactive protein, interlekin-6, uric acid, secretory immunoglobulin A, and testosterone. We assess the sensitivity of rICC estimates to assay type and the unique distributions of the underlying analyte data. We also use simulations to examine the bias, precision, and coverage probability of rICC estimates calculated for small to large sample sizes. For each analyte, the rICCs revealed that less than 5% of variation in analyte levels was attributable to laboratory-based measurement error. rICC estimates were similar across all analytes despite differences in analyte levels, average intra-assay coefficients of variation, and in the distributional properties of the data. Guidelines for calculating rICC are provided to enable investigators and laboratory staff to apply this metric and more accurately quantify, and communicate, the magnitude of laboratory-based measurement error in their data. By helping investigators scale measurement error relative to more scientifically meaningful variability between biological replicates, the application of the rICC has the potential to influence research strategies and tactics such that resources (e.g., finances, effort, number/volume of biospecimens) are allocated more efficiently and effectively.

Theory suggests that early experiences may calibrate the threshold activity of the hypothalamus-pituitary-adrenal axis in childhood. Particularly challenging or particularly supportive environments are posited to manifest in heightened physiological sensitivity to context. Using longitudinal data from the Family Life Project (N = 1,292), we tested whether links between maternal sensitivity and hypothalamus-pituitary-adrenal axis activity aligned with these predictions. Specifically, we tested whether the magnitude of the within-person relation between maternal sensitivity and childrens cortisol levels, a proxy for physiological sensitivity to context, was especially pronounced for children who typically experienced particularly low or high levels of maternal sensitivity over time. Our results were consistent with these hypotheses. Between children, lower levels of mean maternal sensitivity (7-24 months) were associated with higher mean cortisol levels across this period (measured as a basal sample collected at each visit). However, the magnitude and direction of the within-person relation was contingent on childrens average levels of maternal sensitivity over time. Increases in maternal sensitivity were associated with contemporaneous cortisol decreases for children with typically low-sensitive mothers, whereas sensitivity increases were associated with cortisol increases for children with typically high-sensitive mothers. No within-child effects were evident at moderate levels of maternal sensitivity.

Cortisol output in response to emotion induction procedures was examined at child age 24 months in a prospective longitudinal sample of 1,292 children and families in predominantly low-income and nonurban communities in two regions of high poverty in the United States. Multilevel analysis indicated that observed emotional reactivity to a mask presentation but not a toy removal procedure interacted with sensitive parenting to predict cortisol levels in children. For children experiencing high levels of sensitive parenting, cortisol output was high among children exhibiting high emotional reactivity and low among children exhibiting low emotional reactivity. For children experiencing low levels of sensitive parenting, cortisol output was unrelated to emotional reactivity.

Psychosocial stressors like intimate partner violence (IPV) exposure are associated with increased risk of childhood asthma. Longitudinal studies have not investigated the role of hypothalamic-pituitary-adrenal (HPA) axis reactivity (and associated alterations in cortisol release) in the child IPV exposure-asthma association. We sought to investigate this association, and to assess whether this relationship differs by child HPA reactivity. This secondary analysis used longitudinal cohort data from the Family Life Project. Participants included 1,292 low-income children and mothers; maternal interview and child biomarker data, including maternal report of IPV and child asthma, and child salivary cortisol obtained with validated stress reactivity paradigms, were collected when the child was 7, 15, 24, 35, and 48 months. Using structural equation modeling, maternal IPV when the child was 7 months of age predicted subsequent reports of childhood asthma (B=0.18, p=.002). This association differed according to the childs HPA reactivity status, with IPV exposed children who were HPA reactors at 7 and 15 months of age--defined as a ≥10% increase in cortisol level twenty minutes post peak arousal during the challenge tasks and a raw increase of at least .02μg/dl--being significantly at risk for asthma (7 months: B=0.17, p=.02; 15 months: B=0.17, p=.02). Our findings provide support that children who are physiologically reactive are the most vulnerable to adverse health outcomes when faced with environmental stressors.

Left censoring in salivary bioscience data occurs when salivary analyte determinations fall below the lower limit of an assay's measurement range. Conventional statistical approaches for addressing censored values (i.e., recoding as missing, substituting or extrapolating values) may introduce systematic bias. While specialized censored data statistical approaches (i.e., Maximum Likelihood Estimation, Regression on Ordered Statistics, Kaplan-Meier, and general Tobit regression) are available, these methods are rarely implemented in biobehavioral studies that examine salivary biomeasures, and their application to salivary data analysis may be hindered by their sensitivity to skewed data distributions, outliers, and sample size. This study compares descriptive statistics, correlation coefficients, and regression parameter estimates generated via conventional and specialized censored data approaches using salivary C-reactive protein data. We assess differences in statistical estimates across approach and across two levels of censoring (9% and 15%) and examine the sensitivity of our results to sample size. Overall, findings were similar across conventional and censored data approaches, but the implementation of specialized censored data approaches was more efficient (i.e., required little manipulations to the raw analyte data) and appropriate. Based on our review of the findings, we outline preliminary recommendations to enable investigators to more efficiently and effectively reduce statistical bias when working with left-censored salivary biomeasure data.

The relation of the cumulative experience of poverty in infancy and early childhood to child cortisol at age 48 months was examined in a prospective longitudinal sample of children and families (N=1292) in predominantly low-income and rural communities in two distinct regions of the United States. Families were seen in the home for data collection and cumulative experience of poverty was indexed by parent reported income-to-need ratio and household chaos measures collected between child ages 2 months and 48 months. For the analysis presented here, three saliva samples were also collected over an approximate 90 min interval at child age 48 months and were assayed for cortisol. ECG data were also collected during a resting period and during the administration of a mildly challenging battery of cognitive tasks. Mixed model analysis indicated that child cortisol at 48 months decreased significantly over the sampling time period and that cumulative time in poverty (number of years income-to-need less than or equal to 1) and cumulative household chaos were significantly related to a flatter trajectory for cortisol change and to an overall higher level of cortisol, respectively. Findings also indicated that respiratory sinus arrhythmia derived from the ECG data moderated the association between household chaos and child cortisol and that increase in respiratory sinus arrhythmia during the cognitive task was associated with an overall lower level of cortisol at 48 months.