Bayesian inference for psychology. Part II: Example applications with JASP

Bayesian hypothesis testing presents an attractive alternative to p value hypothesis testing. Part I of this series outlined several advantages of Bayesian hypothesis testing, including the ability to quantify evidence and the ability to monitor and update this evidence as data come in, without the need to know the intention with which the data were collected. Despite these and other practical advantages, Bayesian hypothesis tests are still reported relatively rarely. An important impediment to the widespread adoption of Bayesian tests is arguably the lack of user-friendly software for the run-of-the-mill statistical problems that confront psychologists for the analysis of almost every experiment: the t-test, ANOVA, correlation, regression, and contingency tables. In Part II of this series we introduce JASP (http://www.jasp-stats.org), an open-source, cross-platform, user-friendly graphical software package that allows users to carry out Bayesian hypothesis tests for standard statistical problems. JASP is based in part on the Bayesian analyses implemented in Morey and Rouder’s BayesFactor package for R. Armed with JASP, the practical advantages of Bayesian hypothesis testing are only a mouse click away.     

Altered stress responses in children exposed to early adversity: a systematic review of salivary cortisol studies

Pathological stress responses are implicated in numerous disorders. Hypothalamic-pituitary-adrenal axis function is influenced by gene-environment interaction, with early-life environmental adversity having long-lasting effects. We examine the evidence that, in humans, these effects are apparent from infancy. We systematically reviewed published findings on cortisol response to a stressor, in 0-5-year-olds already exposed to adversity. Adversity was defined as a negative environmental influence present post-conception. We searched Ovid MEDLINE (1950-May 2010), EMBASE (1980-May 2010) and PsychINFO (1806-May 2010). We included peer-reviewed, English language studies that analysed salivary cortisol before and after a standardised stressor. We identified 30 studies, of which 27 reported a significant effect of adversity on the cortisol response to stress. Six of these demonstrated an effect of prenatal substance exposure. Thirteen studies found that psychosocial adversity increased cortisol reactivity. Three studies reported that cortisol reactivity could be normalised by intervention programmes. The studies were heterogeneous, both in nature of adversity studied and in stressor used, precluding meta-analysis and assessment of publication bias. Our review presents evidence that adversity disrupts the stress response from an early age. Longitudinal studies are required to determine whether effects persist, alter with time, or are reversible with intervention.     

Accounting for fluctuations in body dissatisfaction

The present study evaluated whether the strength of relationship between contextual cues (presence of company and mood) and state body dissatisfaction varied as a function of individual differences in key trait measures (body shame, body surveillance tendencies, internalization of appearance standards, and trait affect) which have been linked to trait body dissatisfaction. Fifty-five undergraduate women completed a questionnaire containing the trait-based measures and then carried a Personal Digital Assistant (PDA) for a 7-day period. The PDA prompted participants six times daily to self-report their current mood and state body dissatisfaction. Multi-level modeling revealed that individual differences in body shame predicted inter-individual variability in the strength of the relationships between presence of company and state body dissatisfaction, and positive mood and state body dissatisfaction. Trait positive affect also explained variance in the positive mood state-body dissatisfaction relationship. The implications of the findings for prevention of body image disturbances are discussed.     

Sexuality and Exercise Motivations: Are Gay Men and Heterosexual Women Most Likely to be Motivated by Concern About Weight and Appearance?

This study was designed to investigate the relationship between sexuality and exercise motivations in 93 British bar staff. Participants who self-identified as heterosexual, gay, or lesbian completed the revised version of the Exercise Motivations Inventory and reported exercise frequency. Heterosexual men scored lower on appearance motives than did heterosexual women and gay men, higher on enjoyment motives than did gay men, and higher on competition motives than did women and gay men. Men were significantly less likely than women to be motivated by weight management. Heterosexual men also reported exercising significantly more frequently than the other three groups. Suggestions for targeted exercise promotion initiatives are discussed.     

Cone excitation ratios correlate with color discrimination performance in the horse (Equus caballus)

Six horses (Equus caballus) were trained to discriminate color from grays in a counterbalanced sequence in which lightness cues were irrelevant. Subsequently, the pretrained colors were presented in a different sequence. Two sets of novel colors paired with novel grays were also tested. Performance was just as good in these transfer tests. Once the horse had learned to select the chromatic from the achromatic stimulus, regardless of the specific color, they were immediately able to apply this rule to novel stimuli. In terms of the underlying visual mechanisms, the present study showed for the first time that the spectral sensitivity of horse cone photopigments, measured as cone excitation ratios, was correlated with color discrimination performance, measured as accuracy, repeated errors, and latency of approach.     

A randomized controlled trial of cognitive behavior therapy for borderline personality disorder: rationale for trial, method, and description of sample

This paper describes the rationale for a randomized controlled trial, comparing cognitive behavior therapy in addition to treatment as usual with treatment as usual alone, for borderline personality disorder. Previous pioneering randomized controlled trials of psychotherapies have suffered from methodological weaknesses and have not always been reported clearly to allow adequate evaluation of either the individual study or comparisons across studies to be undertaken. We report on the recruitment and randomization, design, and conduct of an ongoing randomized controlled trial of one hundred and six patients with borderline personality disorder. Primary and secondary hypotheses and their planned analyses are stated. The baseline characteristics of 106 patients meeting diagnostic criteria for borderline personality disorder are described.     

Predictors and outcomes of early motherhood in the Australian Longitudinal Study on Women's Health

Early motherhood is identified as a social problem, and having children at an early age is assumed to lead to psychological distress, welfare dependence and socioeconomic disadvantage. Analysis of responses from 9,689 young participants in the Australian Longitudinal Study on Women's Health was used to examine predictors and outcomes of early motherhood in Australia. Survey 1 (1996, aged 18 - 23) and Survey 2 (2000, aged 22 - 27), were used to categorize women as Childless, Existing Mothers (before Survey 1) and New Mothers (became mothers before Survey 2). Multivariate logistic regressions provided comparisons on sociodemographics, gynaecological variables, psychological wellbeing and health behaviours. Survey 1 data show that Existing Mothers experience socioeconomic disadvantages and unhealthy lifestyles. However, those who will go on to become mothers earlier than their peers already experience similar disadvantages. Further, the Survey 2 data show that, when these pre-existing disadvantages are controlled for, the additional deficits experienced by early mothers are relatively minor. Social disadvantage predisposes women to become mothers early, and to adopt unhealthy behaviours. However, young Australian women cope well with the challenges of early motherhood. In the longer term, unhealthy lifestyles and low education may lead to ill health and disadvantage, but early motherhood is not the initiator of this trajectory.