Phenotypic and Discordant-Monozygotic Analyses of Stress and Perceived Social Support as Antecedents to or Sequelae of Risk for Depression
The associations between social support and depression, and between stress and depression have been the subject of considerable research, and although this has included longitudinal designs, these have rarely controlled for genetic effects that mediate these associations. The sample comprised 7,356 female and 4,882 male participants aged 18-95 from the Australian NHMRC Twin Registry (ATR). Of these, between 100 and 324 female pairs and between 41 and 169 male pairs, depending on the measure, were monozygotic (MZ) pairs discordant for depression. We use the co-twin control design in combination with prospective analyses to explore the association between a composite of predictors (perceived social support, stress, and support × stress) and depression. With familial effects included, both perceived support and stress were antecedents to, and sequelae of, depression, but no stress-buffering occurred. With familial effects controlled, stress was a sequela of a prior depressive episode, and neither lack of support nor stress were antecedents to depression, though their interaction approached significance for males. The male twin who later became depressed had previously reported lower perceived support in the face of multiple stressors compared to his co-twin who did not become depressed. We show that associations commonly observed with prospective designs are partly due to familial factors.
Does Classroom Separation Affect Twins' Reading Ability in the Early Years of School?
In this article we report on reading ability of twin children in kindergarten to Grade 2 as a function of whether members of the pairs are assigned to the same or different classrooms. All analyses were run using mixed model regressions to account for the interdependence between twin pairs. The samples, total N = 1505, are from Australia and the United States. We found a close-to-significant difference in favor of same-class children in kindergarten and Grade 1. However, when results were adjusted to take account of pre-existing differences in disruptive behavior and in preliteracy ability, the class assignment effects disappeared. We suggest that these pre-existing differences, particularly disruptive behavior, are influencing decisions about whether to separate twins or not and also affecting early reading performance, a conclusion supported by significant correlations between the behavioral measures, preliteracy, and school-based reading. We conclude that, on average, early literacy in twins is not directly affected by their assignment to the same or different classrooms.
Differential Influences of Genes and Environment Across the Distribution of Reading Ability
We partitioned early childhood reading into genetic and environmental sources of variance and examined the full distribution of ability levels from low through normal to high as computed by quantile regression. The full sample comprised twin pairs measured at preschool (n = 977), kindergarten (n = 1028), grade 1 (n = 999), and grade 2 (n = 1000). Quantile regression analyses of the full distribution of literacy ability showed genetic influence in all grades from preschool to grade 2. At preschool, the low end of the distribution had higher genetic influence than the high end of the distribution and the shared environment influence was the opposite. These shared environment influences of preschool became insignificant with formal schooling. This suggests that higher scores in pre-literacy skills (preschool) are more influenced by shared environment factors, though these are short-lived. This study discusses the factors that may be influencing the results.
Estimating the Extent of Parameter Bias in the Classical Twin Design: A Comparison of Parameter Estimates From Extended Twin-Family and Classical Twin Designs
The 'classical twin design' (CTD) circumvents parameter indeterminacy by assuming (1) negligible higher-order epistasis; and (2) either nonadditive genetic or common environmental effects are nonexistent, creating two potential sources of bias (Eaves et al., 1978; Grayson, 1989). Because the extended 'twin-family design' (ETFD) uses many more unique covariance observations to estimate parameters, common environmental and nonadditive genetic parameters can be simultaneously estimated. The ETFD thereby corrects for what is likely to be the largest of the two sources of bias in CTD parameter estimates (Keller & Coventry, 2005). In the current paper, we assess the extent of this and other potential sources of bias in the CTD by comparing all published ETFD parameter estimates to CTD parameter estimates derived from the same data. CTD estimates of the common environment were lower than ETFD estimates of the common environment for some phenotypes, but for other phenotypes (e.g., stature in females and certain social attitudes), what appeared as the common environment was resolved to be assortative mating in the ETFD. On average, CTD estimates of nonadditive genetic factors were 43% lower, and additive genetic factors 63% higher, than ETFD estimates. However, broad-sense heritability estimates from the CTD were only 18% higher than ETFD estimates, highlighting that the CTD is useful for estimating broad-sense but not narrow-sense heritability. These results suggest that CTD estimates can be misleading when interpreted literally, but useful, albeit coarse, when interpreted properly.
Genome-wide association for major depressive disorder: a possible role for the presynaptic protein piccolo
Major depressive disorder (MDD) is a common complex trait with enormous public health significance. As part of the Genetic Association Information Network initiative of the US Foundation for the National Institutes of Health, we conducted a genome-wide association study of 435 291 single nucleotide polymorphisms (SNPs) genotyped in 1738 MDD cases and 1802 controls selected to be at low liability for MDD. Of the top 200, 11 signals localized to a 167 kb region overlapping the gene piccolo (PCLO, whose protein product localizes to the cytomatrix of the presynaptic active zone and is important in monoaminergic neurotransmission in the brain) with P-values of 7.7×10⁻⁷ for rs2715148 and 1.2×10⁻⁶ for rs2522833. We undertook replication of SNPs in this region in five independent samples (6079 MDD independent cases and 5893 controls) but no SNP exceeded the replication significance threshold when all replication samples were analyzed together. However, there was heterogeneity in the replication samples, and secondary analysis of the original sample with the sample of greatest similarity yielded P=6.4×10⁻⁸ for the nonsynonymous SNP rs2522833 that gives rise to a serine to alanine substitution near a C2 calcium-binding domain of the PCLO protein. With the integrated replication effort, we present a specific hypothesis for further studies.
The Sky is Falling: Exploring Anticipatory Traumatic Reaction
In recent years, the global community has suffered uncertainty and threats to safety due to a variety of events, including terrorist attacks, large-scale accidents, natural disasters, and international conflicts. Indirect engagement with these events is made possible through the media. Numerous studies have found negative psychological outcomes following indirect exposure to trauma, either via media coverage or through care of people directly impacted. If media has the potential to effect even small negative changes in psychological health, then cumulative or more intense exposure might lead to more substantive effects.
This thesis explored whether trauma-related media consumption and ensuing social discussions may trigger a unique form of distress, referred to as Anticipatory Traumatic Reaction (ATR). This construct is based on the dual scaffold of (1) the diagnostic criteria of posttraumatic stress disorder (PTSD) considered sub-clinically and (2) emotions, cognitions, and behaviours that have been associated with secondary exposure to trauma. Specifically, ATR is conceptualised as involving people overestimating future risk (for themselves or significant others) of traumatic events presented in the media and experiencing distress relating to feared outcomes. Affected individuals might engage in thoughts or behaviours designed to reduce uncertainty or prepare for adverse events and experience disruptions in day-to-day functioning.
A total of six studies (reported in the format of five stand-alone articles) were conducted. Study 1 was a quantitative meta-analysis of experimental studies that evaluated the overall effect of threat-related media on psychological outcomes. This study confirmed the association between trauma-related media exposure and negative psychological outcomes and provided evidence to support a causal pathway. Studies 2 and 3 (reported in a single journal article) generated a new psychometric measure to assess the novel construct of ATR and found preliminary evidence of this form of distress in a general population of Australians. Study 2 used exploratory and confirmatory factor analysis to construct a scale with three latent variables (feelings, preparation, and disruptions relating to ATR) and correlational analyses found evidence of convergent and discriminant validity for the scale. Study 3 provided additional validation of the scale, examined links with conceptually related variables pertaining to media consumption, and provided evidence for ATR as a construct that, despite some overlap, is separate and distinct from PTSD. The results also indicated that higher levels of ATR are associated with a greater degree of engagement with threat-related media and social discussions. Further, the results suggested that younger people might be at greater risk of ATR than older people, and that this may be partially accounted for by a greater proportion of social media news-gathering by younger people.
Study 4 explored possible links between ATR and a reaction to another form of secondary exposure to trauma – compassion fatigue, which occurs as a consequence of providing a caring role for traumatised individuals. The results suggested that high levels of ATR may exacerbate levels of depression, anxiety, and stress, potentially putting care workers at greater risk of job burnout. Study 5, a meta-analytic review of the efficacy of mindfulness interventions for treating PTSD, indicated that, across studies, mindfulness was effective in reducing symptoms of PTSD. Given some symptomatic and conceptual similarities between PTSD and ATR, this finding pointed to mindfulness as a potentially useful technique for mitigating ATR. The final study, Study 6, assessed proposed risk factors for ATR and used an online experiment with random assignment to test a series of brief interventions to attenuate ATR. The findings suggested that risk factors for experiencing higher levels of ATR included being female, being younger, living with a mental illness, repetitive negative thinking, intolerance of uncertainty, personal distress empathy, fantasy empathy, and a concern about world politics. Both a cognitive intervention to address probability neglect and a mindfulness intervention showed promise in attenuating momentary ATR.
The current research provides preliminary evidence for ATR as a newly identified psychological condition that may occur for some people in response to media exposure and social discussions of disasters and large-scale threats. If, as suggested by the results of this research, people with existing mental illness are at greater risk for ATR and that ATR might exacerbate existing symptoms, it will be important to identify vulnerable subsets of this population so that clinicians can intervene to reduce ATR and limit distress. Because media exposure to traumatic events is a basis for ATR, the findings have implications for presentation of media content. This thesis adds to the body of knowledge in the fields of trauma, social psychology, and clinical practice.
Measuring CHAOS? Evaluating the short-form Confusion, Hubbub And Order Scale
The Confusion, Hubbub and Order Scale (CHAOS) – short form – is a survey tool intended to capture information about home environments. It is widely used in studies of child and adolescent development and psychopathology, particularly twin studies. The original long form of the scale comprised 15 items and was validated in a sample of infants in the 1980s. The short form of the scale was developed in the late 1990s and contains six items, including four from the original scale, and two new items. This short form has not been validated and is the focus of this study. We use five samples (N=10,898) from studies in Australia, the UK, and the USA, to examine the measurement properties of the CHAOS short form. We first compare alternate confirmatory factor models for each group; we next test between-group configural, metric and scalar invariance; finally, we examine predictive validity of the scale in each sample under different conditions. We find evidence that a two-factor configuration of the six items is more appropriate than the commonly used one-factor model. Second, we find measurement non-invariance across groups at the metric invariance step, with items performing differently depending on the sample. By contrast we find longitudinal measurement invariance in two of the three samples with multi-wave data collection on the CHAOS. Finally, we report inconsistent results in tests of predictive validity using family-level socioeconomic status and academic achievement as criterion variables. The results caution the continued use of the short-form CHAOS in its current form and recommend future revisions and development of the scale for use in developmental research.
Differences between the single-event and frequency formats of seasonal-climate-forecast probability
Since the late 1980s, Australian forecasters have used the seasonal climate forecast (SCF) statement 'In the next three months, the probability of getting above median rainfall is 30%.' Study one (n=63) established a baseline of whether laypersons interpreted this statement as forecasting wetter or drier conditions than normal. Although the statement is forecasting a greater likelihood of drier conditions than normal, 76% incorrectly interpreted the statement as forecasting a wetter season than normal. Using testing conditions identical to study one, in study two (n = 71), to improve accuracy, we inserted the word only in the statement (i.e. ' ...probability of getting above median rainfall is only 30%'). While the probability itself had not changed, a drop to just 24% errors suggested participants were ambiguous about how to interpret this probability. A body of research by Gigerenzer and others shows peoples' ability to reason with probabilities is enhanced by frequency probabilities rather than single-event probabilities. Study three (n =51) used the frequency (i.e. 3 in 10) rather than single-event (i.e. 30%) format tested in studies one and two. Only 22% made errors showing participants better understood how to interpret the frequency probability. We discuss formats for presenting the SCF and argue the frequency format more effectively conveys the chance nature of forecasts.
Identical Genes, Unique Environments: A Qualitative Exploration of Persistent Monozygotic-Twin Discordance in Literacy and Numeracy
This study aimed to explore unique environmental factors impacting differential academic trajectories among Australian school students. Monozygotic (MZ) twin pairs who were consistently discordant in results of nationwide standardized tests of reading, numeracy or writing between Grades 3 and 9 were identified. MZ twins control for genes, gender, age, and aspects of the home and school environment shared by twins. Thus, any difference between MZ twins in academic outcomes can be attributed to the unique environment experienced by each twin. From 551 MZ twin pairs with three or four sets of test results, we identified 55 pairs who were substantially and consistently discordant in reading, numeracy or writing between Grades 3 and 9. Parents were contacted for interview, resulting in 40 semi-structured interviews. Qualitative data analysis revealed three major themes, interpreted by parents as possible contributors to persistent academic discordance: biological mechanisms, school-based factors, and personal factors. We discuss implications for educational practice, policy, and research.
Anticipatory Traumatic Reaction and Compassion Fatigue (Thesis Study 4)
This study investigated the relationship and interactions between compassion fatigue and anticipatory traumatic reaction (ATR), both conditions arising from secondary exposure to trauma. Compassion fatigue, which often occurs for caring professionals, involves symptoms of secondary traumatic stress and job burnout. ATR is a future-focused form of distress arising from media reports and social discussions of large-scale negative events and threats. A cohort of 48 youth workers from a not-for-profit company located in the New England region completed measures of secondary traumatic stress, burnout, compassion satisfaction, general distress, and anticipatory traumatic reaction. Surveys were completed via the online Qualtrics platform. Results showed that ATR magnified the relationship between secondary traumatic stress and general distress. Moderated mediation analyses indicated that anticipatory traumatic reaction interacted with general distress in connecting secondary traumatic stress with burnout. High levels of ATR may exacerbate distress, potentially putting care workers at greater risk of burnout.