Comparison of methods for the analysis of relatively simple mediation models

Indirect effects in mediation analyses should not be tested for statistical significance

BACKGROUND AND OBJECTIVE

Mediation analysis is used to gain insight into the mechanisms of exposure-outcome effects by dividing this effect into a direct and an indirect effect. One of the problems of mediation analysis is that in many situations, the standard error of the indirect effect is much lower than the standard errors of the total and direct effect. Because this problem is ignored in the epidemiological literature, the purpose of this paper was to illustrate this problem and to provide an advice regarding the statistical testing of indirect effects in mediation analysis.

METHODS

To illustrate the problem of the estimation of the standard error of the indirect effect two real life datasets and several simulations are used.

RESULTS

The paper shows that the problem of estimating the standard error of the indirect effect was most pronounced when the relationship between exposure and mediator and the relationship between mediator and outcome were equally strong. Furthermore, the magnitude of the estimation problem is different for different strengths of the mediation effect.

CONCLUSION

The indirect effect in mediation analysis should not be tested for statistical significance but the importance of mediation should be evaluated by its clinical relevance.

Sex Differences in Out-of-Hospital Cardiac Arrest Survival Trends

BACKGROUND

Out-of-hospital cardiac arrest survival rates have improved over time. This study established whether improvements were similar for women and men, and to what extent resuscitation characteristics or in-hospital procedures contributed to sex differences in temporal trends.

METHODS AND RESULTS

This retrospective cohort study included 3386 women and 8564 men from North Holland, the Netherlands, who experienced an out-of-hospital cardiac arrest from a cardiac cause in 2005 to 2017. Yearly rates of 30-day survival and secondary outcomes were calculated. Sex differences in temporal trends were evaluated with age-adjusted Poisson regression analysis, including interaction for sex and out-of-hospital cardiac arrest year. Resuscitation characteristics and in-hospital procedures were added to the model, and a spline at 2013 was considered. During the study period, the average 30-day survival was 24.9% in men and 15.7% in women. The 30-day survival rate increased in men (20% to 27.2%; P<0.001) but not in women (15.0% to 11.6%; P=0.40). The increase in the 30-day survival rate was 3% higher per year in men than in women (rate ratio, 1.03 [95% CI, 1.00-1.05]), with a stronger difference after 2013. Men had a larger increase in survival rate to the hospital arrival than women in 2005 to 2013, and, after 2013, an advantage over women in survival rate after hospital arrival. The sex differences were partly explained by differing trends in shockable initial rhythm (eg, adjusted rate ratio, 1.01 [95% CI, 0.99-1.03] for 30-day survival) and provision of in-hospital procedures.

CONCLUSIONS

Changes in rates of 30-day survival, survival to hospital arrival, and, after 2013, survival from hospital arrival to 30 days were more beneficial in men than women. The differences in trends were partly explained by shockable initial rhythm and in-hospital procedures.

The mediating role of attachment and anger: exploring the impact of maternal early-life maltreatment on child abuse potential

Background

Maternal early-life maltreatment (ELM) increases the risk of subsequent child maltreatment, but the underlying mechanisms of these intergenerational effects remain largely unknown. Identifying these mechanisms is crucial for developing preventive interventions that can break the cycle of abuse. Notably, previous research has shown that ELM often results in attachment insecurity and altered anger characteristics. Therefore, this study determines whether these characteristics mediate the relationship between maternal history of ELM and child abuse potential.

Methods

The study sample included 254 mothers, of whom 149 had experienced ELM to at least a moderate degree. Maternal ELM was assessed using the Childhood Experience of Care and Abuse (CECA) interview. Attachment insecurity, trait anger and anger expression, and maternal abuse potential were assessed using the Vulnerable Attachment Questionnaire (VASQ), State-Trait Anger Expression Inventory (STAXI), and Child Abuse Potential Inventory (CAPI), respectively.

Results

The severity of maternal ELM predicted higher child abuse potential, with attachment insecurity and anger suppression mediating this effect. Specifically, higher levels of maternal ELM were associated with greater attachment insecurity and increased anger suppression, resulting in a higher child abuse potential. Although higher levels of trait anger were directly associated with higher child abuse potential, this parameter did not mediate the relationship with ELM. In addition, no significant associations were observed between outwardly expressed anger and ELM or child abuse potential. All analyses were adjusted for maternal mental disorders, years of education, and relationship status.

Discussion

Attachment insecurity and anger suppression may serve as pathways linking the maternal history of ELM to the risk of child abuse, even when considering maternal psychopathology. Overall, our findings indicate that interventions aimed at strengthening attachment and improving anger suppression may be beneficial for all mothers with ELM history and high child abuse potential, not just those who suffer from mental illness.

Questions of value, questions of magnitude: An exploration and application of methods for comparing indirect effects in multiple mediator models

Mediation analysis is widely used to test and inform theory and debate about the mechanism(s) by which causal effects operate, quantitatively operationalized as an indirect effect in a mediation model. Most effects operate through multiple mechanisms simultaneously, and a mediation model is likely to be more realistic when it is specified to capture multiple mechanisms at the same time with the inclusion of more than one mediator in the model. This also allows an investigator to compare indirect effects to each other. After an overview of the mechanics of mediation analysis, we advocate formally comparing indirect effects in models that include more than one mediator, focusing on the important distinction between questions and claims about value (i.e., are two indirect effects the same number?) versus magnitude (i.e., are two indirect effects equidistant from zero or the same in strength?). After discussing the shortcomings of the conventional method for comparing two indirect effects in a multiple mediator model-which only answers a question about magnitude in some circumstances-we introduce several methods that, unlike the conventional approach, always answer questions about difference in magnitude. We illustrate the use of these methods and provide code that implements them in popular software. We end by summarizing simulation findings and recommending which method(s) to prefer when comparing like- and opposite-signed indirect effects.

A Causal Approach to Functional Mediation Analysis with Application to a Smoking Cessation Intervention

The increase in the use of mobile and wearable devices now allows dense assessment of mediating processes over time. For example, a pharmacological intervention may have an effect on smoking cessation via reductions in momentary withdrawal symptoms. We define and identify the causal direct and indirect effects in terms of potential outcomes on the mean difference and odds ratio scales, and present a method for estimating and testing the indirect effect of a randomized treatment on a distal binary variable as mediated by the nonparametric trajectory of an intensively measured longitudinal variable (e.g., from ecological momentary assessment). Coverage of a bootstrap test for the indirect effect is demonstrated via simulation. An empirical example is presented based on estimating later smoking abstinence from patterns of craving during smoking cessation treatment. We provide an R package, funmediation, available on CRAN at https://cran.r-project.org/web/packages/funmediation/index.html, to conveniently apply this technique. We conclude by discussing possible extensions to multiple mediators and directions for future research.

The contribution of prognostic factors to socio-demographic inequalities in breast cancer survival in Victoria, Australia

BACKGROUND

Breast cancer survival in Australia varies according to socio-economic status (SES) and between rural and urban places of residence. Part of this disparity may be due to differences in prognostic factors at the time of diagnosis.

METHODS

Women with invasive breast cancer diagnosed from 2008 until 2012 (n = 14,165) were identified from the Victorian Cancer Registry and followed up for 5 years, with death from breast cancer or other causes recorded. A prognostic score, based on stage at diagnosis, cancer grade, whether the cancer was detected via screening, reported comorbidities and age at diagnosis, was constructed for use in a mediation analysis.

RESULTS

Five-year breast cancer mortality for women with breast cancer who were in the lowest quintile of SES (10.3%) was almost double that of those in the highest quintile (5.7%). There was a small survival advantage (1.7% on average, within each socio-economic quintile) of living in inner-regional areas compared with major cities. About half of the socio-economic disparity was mediated by prognostic factors, particularly stage at diagnosis and the presence of comorbidities. The inner-regional survival advantage was not due to differences in prognostic factors.

CONCLUSIONS

Part of the socio-economic disparity in breast cancer survival could be addressed by earlier detection in, and improved general health for, more disadvantaged women. Further research is required to identify additional causes of socio-economic disparities as well as the observed inner-regional survival advantage.

Mild Traumatic Brain Injury and Functional Outcome in Older Adults: Pain Interference But Not Cognition Mediates the Relationship Between Traumatic Injury and Functional Difficulties

OBJECTIVE

To examine functional status of older people 3 months after mild traumatic brain injury (mTBI) and identify whether pain interference or cognition mediates any relationship found between injury status and functional outcomes.

SETTING

Patients admitted to a Melbourne-based emergency department.

PARTICIPANTS

Older adults 65 years and older: 40 with mTBI, 66 with orthopedic injury without mTBI (TC), and 47 healthy controls (CC) without injury.

DESIGN

Observational cohort study.

MAIN MEASURES

Functional outcome was measured using the World Health Organization Disability Assessment Schedule (WHODAS 2.0) and single- and dual-task conditions of the Timed-Up-and-Go task. Pain interference and cognitive performance at 3 months post-injury were examined as mediators of the relationship between injury status (injured vs noninjured) and functional outcome.

RESULTS

Patients with mTBI and/or orthopedic injury reported greater difficulties in overall functioning, including community participation, compared with noninjured older people (CC group). Both trauma groups walked slower than the CC group on the mobility task, but all groups were similar on the dual-task condition. Pain interference mediated the relationship between injury status and overall functioning [ b = 0.284; 95% CI = 0.057, 0.536), community participation ( b = 0.259; 95% CI = 0.051, 0.485), and mobility ( b = 0.116; 95% CI = 0.019, 0.247). However, cognition did not mediate the relationship between injury status and functional outcomes.

CONCLUSIONS

Three months after mild traumatic injury (with and without mTBI), patients 65 years and older had greater functional difficulties compared with noninjured peers. Pain interference, but not cognition, partially explained the impact of traumatic injury on functional outcomes. This highlights the importance of reducing pain interference for older patients after injury (including mTBI) to support better functional recovery.

Factors related to positive attitudes toward palliative care: Direct and indirect effects of self-care self-efficacy, knowledge, and beliefs

CONTEXT

Knowledge, beliefs, and attitudes toward palliative care (PC) constitute barriers to its access. Few studies have focused on the intrinsic relationship between these variables, and none has examined the relationship between them and self-care self-efficacy.

OBJECTIVE

To examine the direct and indirect effects of self-care self-efficacy, knowledge, and beliefs on attitudes toward PC.

METHODS

A cross-sectional predictive study was conducted. Self-care self-efficacy, knowledge, attitudes, and beliefs about PC were analyzed using information from the Health Information National Trends Survey (HINTS 5, cycle 2, 2018). Data from 1,162 participants were considered. Structural equation modeling (SEM) was used to represent the statistical mediation model with latent and observable variables.

RESULTS

The structural model presents positive coefficients indicating that self-care self-efficacy significantly predicts knowledge (β = 0.127, p < 0.001) and beliefs (β = 0.078, p = 0.023). Similarly, knowledge is associated with attitudes (β = 0.179, p < 0.001) and beliefs (β = 0.213, p < 0.001). The beliefs measure is also significantly related to attitudes (β = 0.474, p < 0.001). In addition, this structural multiple mediation model shows optimal goodness-of-fit indices: χ2/df = 3.49, CFI = 0.983, TLI = 0.976, RMSEA = 0.046 [90% CI: 0.037-0.056], SRMR = 0.038.

CONCLUSION

Self-care self-efficacy is significantly associated with knowledge and beliefs about PC, which in turn are related to each other. Altogether, these variables predict positive attitudes toward PC. Understanding the relationship between these variables is relevant for targeting-specific populations and designing timely strategies to improve access to PC.

Correcting the Bias Correction for the Bootstrap Confidence Interval in Mediation Analysis

The bias-corrected bootstrap confidence interval (BCBCI) was once the method of choice for conducting inference on the indirect effect in mediation analysis due to its high power in small samples, but now it is criticized by methodologists for its inflated type I error rates. In its place, the percentile bootstrap confidence interval (PBCI), which does not adjust for bias, is currently the recommended inferential method for indirect effects. This study proposes two alternative bias-corrected bootstrap methods for creating confidence intervals around the indirect effect: one originally used by Stine (1989) with the correlation coefficient, and a novel method that implements a reduced version of the BCBCI's bias correction. Using a Monte Carlo simulation, these methods were compared to the BCBCI, PBCI, and Chen and Fritz (2021)'s 30% Winsorized BCBCI. The results showed that the methods perform on a continuum, where the BCBCI has the best balance (i.e., having closest to an equal proportion of CIs falling above and below the true effect), highest power, and highest type I error rate; the PBCI has the worst balance, lowest power, and lowest type I error rate; and the alternative bias-corrected methods fall between these two methods on all three performance criteria. An extension of the original simulation that compared the bias-corrected methods to the PBCI after controlling for type I error rate inflation suggests that the increased power of these methods might only be due to their higher type I error rates. Thus, if control over the type I error rate is desired, the PBCI is still the recommended method for use with the indirect effect. Future research should examine the performance of these methods in the presence of missing data, confounding variables, and other real-world complications to enhance the generalizability of these results.

Cost drivers associated with diffuse large B-cell lymphoma (DLBCL) in Japan: A structural equation model (SEM) analysis

Diffuse large B-cell lymphoma (DLBCL) is an aggressive non-Hodgkin’s lymphoma of increasing prevalence in Japan. However, patients with relapsed or refractory disease to first line treatment (rrDLBCL) have been found to shoulder greater economic burden and have poor survival with subsequent lines of therapy. The relative impact of individual patient attributes on total medical cost among patients with rrDLBCL receiving second or third line (2L/3L) therapy was assessed. Structural equation modelling was used to identify potential cost drivers of total medical costs incurred by treatment and procedures in a Japanese retrospective claims database. From the database, rrDLBCL patients on 2L or 3L of treatment were grouped into respective cohorts. The mean [median] (SD) total medical cost of care for the 2L cohort was 73,296.40 [58,223.11] (58,409.79) US dollars (USD) and 75,238.35 [60,477.31] (59,583.66) USD for the 3L cohort. The largest total effect on medical cost in both cohorts was length of hospital stay (LOS) (β: 0.750 [95%CI: 0.728, 0.772] vs β: 0.762 [95%CI: 0.729, 0.794]). Length of hospital stay and potential heart disease complications due to line of treatment were the primary drivers of total cost for patients who had received at least 2L or 3L therapy for rrDLBCL.

The association between gender-related characteristics and type 2 diabetes risk in a multi-ethnic population: The HELIUS study

BACKGROUND AND AIMS

Men and women have different type 2 diabetes mellitus (T2DM) risks, which have been reported across populations of different ethnicity. Where differences in T2DM risk for sex (biological) have been studied, research on gender (socio-cultural) and T2DM risk is lacking. We explored, in a multi-ethnic population, the association of six gender-related characteristics with incident T2DM over 3 years, and the mediation by known risk factors for T2DM.

METHODS AND RESULTS

We included 9605 women and 7080 men of the multi-ethnic HELIUS study (Amsterdam, the Netherlands). We studied associations between gender-related characteristics and incident T2DM, using Cox regression. After a median of 3.0 years (IQR 2.0; 4.0), 198 (2.1%) women and 137 (1.9%) men developed T2DM. A lower T2DM risk was observed in those not being the primary earner (HR 0.67; 95% CI 0.47; 0.93) and a higher desired level of social support (HR 0.62; 95% CI 0.44; 0.87). Hours spent on household work, home repairs, type of employment and male- or female-dominated occupation were not associated with T2DM incidence. No evidence for effect modification by biological sex or ethnicity was found. Known risk factors of T2DM did not mediate the observed associations.

CONCLUSION

Gender-related characteristics, not being the primary earner and a higher desired social support were associated with reduced T2DM risk, and this was not mediated by known risk factors for T2DM.

Relationship Between Satisfaction With Medical Care, Physical Health, and Emotional Well-Being in Adult Men: Mediating Role of Communication

Background:

Non-communicable diseases and psychiatric pathologies are the health problems that most affect the population in the United States.

Objective:

This study aimed to examine the mediating role of patient-centered communication (PCC) in the relationship between satisfaction with medical care, physical health, and emotional well-being in American men.

Methods:

A cross-sectional - predictive study was carried out. The variables analyzed were satisfaction with medical care, physical health, and emotional well-being. Information from the Health Information National Trends Survey Data (HINTS) was used; HINTS 5, cycle 3 (collected between January and June 2019) and 4 (2020). Data from 3338 men were considered (mean age: M = 55.40, SD = 19.53). Data analyses were carried out using structural equation modeling (SEM) to represent the statistical mediation model with latent and observable variables.

Results:

Analyses showed that the variables were significantly related (P < .01). In the mediation model, there is evidence that satisfaction predicts communication (β = .764, P < .001) and this, in turn, is related to physical health (β = .079, P = .007) and emotional well-being (β = .145, P < .001). In addition, the standardized estimates of the structural multiple mediation model presented acceptable goodness-of-fit indices: χ²/gl = 2.24, CFI = 0.999, TLI = 0.999, RMSEA = 0.019 [90% CI: 0.013-0.022], SRMR = 0.018.

Conclusion:

Patient-centered communication plays a significant dual mediating role in the relationship between satisfaction with medical care, physical health, and emotional well-being, respectively. Therefore, PCC is essential in healthcare for American men.

Resilience as a Mediator of the Association between Spirituality and Self-Management among Older People with Chronic Obstructive Pulmonary Disease

This study examined the mediating effect of resilience in the relationship between spirituality and self-management among older people with chronic obstructive pulmonary disease (COPD). The participants were 151 older people with COPD in four general hospitals in Jiangsu Province, China. Data were collected from September 2020 to May 2021 using a questionnaire developed by the investigator, the Function Assessment of Chronic Illness Therapy-Spiritual Scale (FACIT-SP-12), 10-item Connor-Davidson Resilience Scale (CD-RISC-10), and COPD Self-Management Scale (CSMS). One-way ANOVA and t-test were used to compare the level of self-management in patients with different sociodemographic and clinical characteristics. Partial correlation analysis was used to explore the correlation between spirituality, resilience, and self-management. Hierarchical multiple regression analyses were performed to examine the contribution of spirituality and resilience to the prediction of self-management. A bootstrapping test was implemented using the SPSS PROCESS macro to test the statistical significance of the mediating effect. There was a pairwise positive correlation between spirituality, resilience, and self-management. Resilience mediated the relationship between spirituality and self-management. These findings suggested that resilience interventions could be incorporated into future COPD self-management interventions to better improve self-management and health outcomes. Moreover, resilience should be an important component of healthy aging initiatives.

Statistical Mediation Analysis for Models with a Binary Mediator and a Binary Outcome: the Differences Between Causal and Traditional Mediation Analysis

Mediation analysis is an important statistical method in prevention research, as it can be used to determine effective intervention components. Traditional mediation analysis defines direct and indirect effects in terms of linear regression coefficients. It is unclear how these traditional effects are estimated in settings with binary variables. An important recent methodological advancement in the mediation analysis literature is the development of the causal mediation analysis framework. Causal mediation analysis defines causal effects as the difference between two potential outcomes. These definitions can be applied to any mediation model to estimate natural direct and indirect effects, including models with binary variables and an exposure-mediator interaction. This paper aims to clarify the similarities and differences between the causal and traditional effect estimates for mediation models with a binary mediator and a binary outcome. Causal and traditional mediation analyses were applied to an empirical example to demonstrate these similarities and differences. Causal and traditional mediation analysis provided similar controlled direct effect estimates, but different estimates of the natural direct effects, natural indirect effects, and total effect. Traditional mediation analysis methods do not generalize well to mediation models with binary variables, while the natural effect definitions can be applied to any mediation model. Causal mediation analysis is therefore the preferred method for the analysis of mediation models with binary variables.

Mediation analysis methods used in observational research: a scoping review and recommendations

Background

Mediation analysis methodology underwent many advancements throughout the years, with the most recent and important advancement being the development of causal mediation analysis based on the counterfactual framework. However, a previous review showed that for experimental studies the uptake of causal mediation analysis remains low. The aim of this paper is to review the methodological characteristics of mediation analyses performed in observational epidemiologic studies published between 2015 and 2019 and to provide recommendations for the application of mediation analysis in future studies.

Methods

We searched the MEDLINE and EMBASE databases for observational epidemiologic studies published between 2015 and 2019 in which mediation analysis was applied as one of the primary analysis methods. Information was extracted on the characteristics of the mediation model and the applied mediation analysis method.

Results

We included 174 studies, most of which applied traditional mediation analysis methods (n = 123, 70.7%). Causal mediation analysis was not often used to analyze more complicated mediation models, such as multiple mediator models. Most studies adjusted their analyses for measured confounders, but did not perform sensitivity analyses for unmeasured confounders and did not assess the presence of an exposure-mediator interaction.

Conclusions

To ensure a causal interpretation of the effect estimates in the mediation model, we recommend that researchers use causal mediation analysis and assess the plausibility of the causal assumptions. The uptake of causal mediation analysis can be enhanced through tutorial papers that demonstrate the application of causal mediation analysis, and through the development of software packages that facilitate the causal mediation analysis of relatively complicated mediation models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-021-01426-3.

Cardiac sympathetic burden reflects Parkinson disease burden, regardless of high or low orthostatic blood pressure changes

Reduced uptake of ¹²³I-meta-iodobenzylguanidine (¹²³I-MIBG) and orthostatic hypotension (OH) are independently associated with worse clinical outcomes of Parkinson's disease (PD). However, their interactive influence on PD has not been studied. The role of ¹²³I-MIBG myocardial uptake, as a biomarker of PD severity, was investigated, conditional on the mediating effects of OH. A total of 227 PD patients were enrolled. Their motor and nonmotor aspects were assessed with standardized tools. Global disease burden was estimated by averaging the scaled z-scores of the assessment tools. Every patient went through ¹²³I-MIBG scan, and OH was evaluated with the head-up tilt-test. The mediating role of orthostatic blood pressure changes (ΔBP) on the association between cardiac sympathetic denervation and disease burden was investigated. Low heart-to-mediastinum (H/M) ratio with less than 1.78 was seen in 69.6% of the patient population, and 22.9% of patients had OH. Low H/M ratio was associated with OH, and these patients had worse disease burden than subjects with normal ¹²³I-MIBG uptake (global composite z-score: normal ¹²³I-MIBG vs. abnormal ¹²³I-MIBG; -0.3 ± 0.5 vs. 0.1 ± 0.7; p < 0.001). The mediation models, controlled for age and disease duration, revealed that the delayed H/M ratio and global composite score were negatively associated, irrespective of orthostatic ΔBP. Adverse relationship between cardiac sympathetic denervation and disease burden was shown without any interference from orthostatic blood pressure fluctuations. This result suggested that extracranial cardiac markers might reflect disease burden, regardless of labile blood pressure influence.

Assessing the Robustness of Mediation Analysis Results Using Multiverse Analysis

There is an increasing awareness that replication should become common practice in empirical studies. However, study results might fail to replicate for various reasons. The robustness of published study results can be assessed using the relatively new multiverse-analysis methodology, in which the robustness of the effect estimates against data analytical decisions is assessed. However, the uptake of multiverse analysis in empirical studies remains low, which might be due to the scarcity of guidance available on performing multiverse analysis. Researchers might experience difficulties in identifying data analytical decisions and in summarizing the large number of effect estimates yielded by a multiverse analysis. These difficulties are amplified when applying multiverse analysis to assess the robustness of the effect estimates from a mediation analysis, as a mediation analysis involves more data analytical decisions than a bivariate analysis. The aim of this paper is to provide an overview and worked example of the use of multiverse analysis to assess the robustness of the effect estimates from a mediation analysis. We showed that the number of data analytical decisions in a mediation analysis is larger than in a bivariate analysis. By using a real-life data example from the Longitudinal Aging Study Amsterdam, we demonstrated the application of multiverse analysis to a mediation analysis. This included the use of specification curves to determine the impact of data analytical decisions on the magnitude and statistical significance of the direct, indirect, and total effect estimates. Although the multiverse analysis methodology is still relatively new and future research is needed to further advance this methodology, this paper shows that multiverse analysis is a useful method for the assessment of the robustness of the direct, indirect, and total effect estimates in a mediation analysis and thereby to inform replication studies.

Distress, Work Satisfaction, and Work Ability are Mediators of the Relation Between Psychosocial Working Conditions and Mental Health-Related Long-Term Sickness Absence

Purpose This study investigated the effects of psychosocial working conditions on mental health-related long-term sickness absence and whether distress, work satisfaction, burnout, engagement, and work ability mediated the associations between psychosocial working conditions and mental health-related long-term sickness absence. Methods This cohort study included 53,833 non-sick listed workers who participated in occupational health surveys between 2010 and 2013. The effects of the individual psychosocial working conditions on mental long-term sickness absence were analyzed using univariable and multivariable logistic regression analyses. Mediation analyses were performed to examine the mediating role of distress, burnout, work satisfaction, engagement, and work ability between psychosocial working conditions and mental long-term sickness absence. The mediation analyses were performed using structural equation modeling. Results Role clarity, cognitive demands, emotional demands, work variety, learning opportunities, and co-worker support were related to mental health-related long-term sickness absence after adjustment for other working conditions. The relationship between emotional demands and mental health-related long-term sickness absence was the strongest, OR 1.304 (p < 0.001, 95% CI 1.135 to 1.498). The relation between psychosocial working conditions and mental health-related long-term sickness absence was mediated by distress, burnout, work satisfaction, engagement, and work ability. Distress was the most important mediator between psychosocial working conditions and mental health-related long-term sickness absence. Conclusions Psychosocial working conditions are related to mental health-related long-term sickness absence. After correction for other working conditions, the association between emotional demands and mental health-related long-term sickness absence was the strongest. Psychosocial working conditions are indirectly related to mental health-related long-term sickness absence through mediation by distress, work satisfaction, and work ability.

Cardiorespiratory Fitness and Performance in Multiple Domains of Executive Functions in School-Aged Adolescents

The objective of this study was to investigate the association between cardiorespiratory fitness (CRF) and performance in multiple domains of executive functions in school–aged adolescents. A sample of 132 adolescents (43% girls) aged 11–16 years were included in this cross–sectional study. Each participant completed a progressive aerobic cardiovascular endurance running (PACER) test, computerized cognitive tasks (Attentional Network, Berg’s Card Sorting, Go/No–Go oddball, Sternberg’s Working Memory, and Tower of London) and questionnaire for daytime sleepiness, as well as other factors that might influence cognitive performance (age, sex, school year, pubertal stage, and body mass index – BMI). Generalized linear model was used to calculate the coefficient estimates (β) and its 95% confidence interval (CI) for the cognitive tasks using PACER laps as a predictor, controlling for potential confounding variables. There was a negatively association of PACER laps with planning (β = –17.1, 95% CI –31.9, –2.3) and solution (β = –44.6, 95% CI –75.1, –14.2) time in performing the Tower of London task, as well as with perseverative errors in performing Berg’s task (β = –0.073, 95% CI –0.133, –0.013). Moderating effect of sex was found for the association of PACER laps with completed categories and perseverative errors in Berg’s task (p < 0.05). Mediating effect of BMI was found for the association between PACER laps and NoGo task, revealing a full mediator accounted for 81% of the total effect mediated (standardized indirect effect, –0.069, 95% CI –0.140, –0.020; standardized direct effect, 0.011, 95% CI –0.149, 0.165). No association was found for Attentional or Sternberg’s tasks. The findings suggest that school–aged adolescents with higher CRF level showed better planning and problem–solving abilities and cognitive flexibility. Additionally, the positive association of CRF with cognitive flexibility was sex–moderated and with inhibitory control was BMI–mediated.

Mediating effects of social support between Type D personality and self-care behaviours among heart failure patients

AIMS

Patients with heart failure exhibit poor adherence to self-care behaviours. Recent studies have shown a link between Type D personality, social support, and self-care behaviours of patients with chronic diseases. However, the mechanisms underlying this relationship have received little empirical attention in those with heart failure. This study aimed to identify the mediating effects of social support in the relationship between Type D personality and self-care behaviours in patients with heart failure.

DESIGN

This study employed a descriptive cross-sectional design.

METHODS

The sample comprised 170 patients aged over 18 years who had been diagnosed with heart failure for over 6 months and visited a tertiary care university hospital in Seoul. From April-July 2019, data were collected through an interview conducted using a structured questionnaire and a review of medical records by two trained research assistants. Multiple regression models were tested using the SPSS PROCESS procedure with bootstrapping to determine the significance of the mediation.

RESULTS

The prevalence of Type D personality in patients with heart failure was 20.0%. Significant associations were identified among Type D personality, social support, and self-care behaviours. Results revealed an indirect effect, suggesting that the effects of Type D personality on self-care behaviours were mediated by social support.

CONCLUSION

Heart failure patients with Type D personality were likely to lack social support, which may have influenced their low adherence to self-care behaviours. Thus, to facilitate long-lasting self-care behaviours, it is vital to provide supportive care or educational programs for patients with Type D personality.

IMPACT

Providing sustainable social support can have a positive impact on the long-term self-care maintenance of patients with heart failure patients who have a Type D personality. Future studies are required to further elucidate the underlying mechanisms of the relationship between Type D personality, social support, and self-care behaviours.

Preoperative inhibitory control predicts weight loss 1 year after bariatric surgery

OBJECTIVE

Executive function (EF) and, in particular, inhibitory control have been associated with weight loss (WL) in behavioural WL treatment for obesity. Few studies have focused on the relationship between preoperative inhibitory control and post-operative WL following bariatric surgery, and the potential mediating role of maladaptive eating behaviours is unclear. The aim of this study was to investigate preoperative executive function as a predictor of WL at 1 year following bariatric surgery. Additionally, we aimed to explore the mediating role of postoperative compulsive grazing in the relationship between inhibitory control and WL.

METHOD

A prospective observational study in which participants completed neuropsychological testing 30 days before and 1 year following surgery (n = 61/80; 76% follow-up). Participants were 80% female, with an average age of 41 years. Approximately 54% underwent gastric bypass, 26% gastric sleeve and 20% had one anastomosis gastric bypass. Regression analyses were employed to examine the relationship between preoperative EF and percentage total weight loss (%TWL), and structural equation modelling was used to examine compulsive grazing as a mediator.

RESULTS

After adjusting for control variables, preoperative inhibitory control explained 8% of the variance in %TWL (p ≤ 0.05). Preoperative working memory was not significantly associated with %TWL. Postoperative compulsive grazing was significantly associated with %TWL (p ≤ 0.05), but did not mediate the association between preoperative inhibitory control and %TWL.

CONCLUSION

The results suggest that preoperative inhibitory control performance is a relevant predictor of postoperative WL and that compulsive grazing is a maladaptive eating behaviour that warrants clinical attention after surgery.

Causal Mediation Programs in R, Mplus, SAS, SPSS, and Stata

Mediation analysis is a methodology used to understand how and why an independent variable (X) transmits its effect to an outcome (Y) through a mediator (M). New causal mediation methods based on the potential outcomes framework and counterfactual framework are a seminal advancement for mediation analysis, because they focus on the causal basis of mediation analysis. There are several programs available to estimate causal mediation effects, but these programs differ substantially in data set up, estimation, output, and software platform. To compare these programs, an empirical example is presented, and a single mediator model with XM interaction was estimated with a continuous mediator and a continuous outcome in each program. Even though the software packages employ different estimation methods, they do provide similar causal effect estimates for mediation models with a continuous mediator and outcome. A detailed explanation of program similarities, unique features, and recommendations are discussed.

Comparing biotic drivers of litter breakdown across stream compartments

Litter breakdown in the streambed is an important pathway in organic carbon cycling and energy transfer in the biosphere that is mediated by a wide range of streambed organisms. However, most research on litter breakdown to date has focused on a small fraction of the taxa that drive it (e.g. microbial vs. macroinvertebrate-mediated breakdown) and has been limited to the benthic zone (BZ). Despite the importance of the hyporheic zone (HZ) as a bioreactor, little is known about what, or who, mediates litter breakdown in this compartment and whether breakdown rates differ between the BZ and HZ. Here, we explore the relationship between litter breakdown and the variation in community structure of benthic and hyporheic communities by deploying two standardized bioassays (cotton strips and two types of commercially available tea bags) in 30 UK streams that encompass a range of environmental conditions. Then, we modelled these assays as a response of the streambed compartment and the biological features of the streambed assemblage (Prokaryota, Protozoa and Eumetazoa invertebrates) to understand the generality and efficiency of litter processing across communities. Litter breakdown was much faster in the BZ compared with the HZ (around 5 times higher for cotton strips and 1.5 times faster for the tea leaves). However, differences in litter breakdown between the BZ and the HZ were mediated by the biological features of the benthos and the hyporheos. Biomass of all the studied biotic groups, α-diversity of Eumetazoa invertebrates and metabolic diversity of Prokaryota were important predictors that were positively related to breakdown coefficients demonstrating their importance in the functioning of the streambed ecosystem. Our study uses a novel multimetric bioassay that is able to disentangle the contribution by Prokaryota, Protozoa and Eumetazoa invertebrates to litter breakdown. In doing so, our study reveals new insights into how organic matter decomposition is partitioned across biota and streambed compartments.

Linking childhood emotional abuse and depressive symptoms: The role of emotion dysregulation and interpersonal problems

Childhood abuse is a major public health problem that has been linked to depression in adulthood. Although different types of childhood abuse often co-occur, few studies have examined their unique impact on negative mental health outcomes. Most studies have focused solely on the consequences of childhood physical or sexual abuse; however, it has been suggested that childhood emotional abuse is more strongly related to depression. It remains unclear which underlying psychological processes mediate the effect of childhood emotional abuse on depressive symptoms. In a cross-sectional study in 276 female college students, multiple linear regression analyses were used to determine whether childhood emotional abuse, physical abuse, and sexual abuse were independently associated with depressive symptoms, emotion dysregulation, and interpersonal problems. Subsequently, OLS regression analyses were used to determine whether emotion dysregulation and interpersonal problems mediate the relationship between childhood emotional abuse and depressive symptoms. Of all types of abuse, only emotional abuse was independently associated with depressive symptoms, emotion dysregulation, and interpersonal problems. The effect of childhood emotional abuse on depressive symptoms was mediated by emotion dysregulation and the following domains of interpersonal problems: cold/distant and domineering/controlling. The results of the current study indicate that detection and prevention of childhood emotional abuse deserves attention from Child Protective Services. Finally, interventions that target emotion regulation skills and interpersonal skills may be beneficial in prevention of depression.

Relationship between aerobic fitness and academic performance: the mediational role of executive function

BACKGROUND

This cross-sectional study investigated whether the relationship between aerobic fitness and academic performance was mediated by executive functioning.

METHODS

A total of 378 children (9-10 years old) from nine primary schools in Stavanger, Norway were included. The children's aerobic fitness was measured by a 10-minute interval-running test; executive function was tested by four cognitive tests (Stroop, Trail Making, Verbal Fluency and Backwards Digit Span). A composite score for executive functions was computed and used in analyses. Academic achievement in reading, mathematics and English was determined using Norwegian national standardized tests.

RESULTS

Bivariate correlation analysis showed the following significant associations: mathematic achievement with executive functions (r=0.48, P=0.001), aerobic fitness with mathematics (r=0.13, P=0.012) and executive functions (r=0.17, P=0.001). A regression-based mediation analysis (PROCESS) with executive function as a mediator variable was conducted. Mediation analysis showed that the relationship between aerobic fitness and mathematic achievement was mediated by executive functions (P<0.001).

CONCLUSIONS

Findings revealed an indirect effect of executive function on the positive relationship between aerobic fitness and mathematic achievement.

On the Interpretation and Use of Mediation: Multiple Perspectives on Mediation Analysis

Mediation analysis has become a very popular approach in psychology, and it is one that is associated with multiple perspectives that are often at odds, often implicitly. Explicitly discussing these perspectives and their motivations, advantages, and disadvantages can help to provide clarity to conversations and research regarding the use and refinement of mediation models. We discuss five such pairs of perspectives on mediation analysis, their associated advantages and disadvantages, and their implications: with vs. without a mediation hypothesis, specific effects vs. a global model, directness vs. indirectness of causation, effect size vs. null hypothesis testing, and hypothesized vs. alternative explanations. Discussion of the perspectives is facilitated by a small simulation study. Some philosophical and linguistic considerations are briefly discussed, as well as some other perspectives we do not develop here.