The coronavirus (COVID-19) pandemic is currently a global health threat attributed to negatively affecting the mental health and well-being of people globally. The purpose of the present study is to examine the mediating role of optimism-pessimism and psychological inflexibility in the relationship of coronavirus stress with psychological problems among Turkish adults. The sample of the study included 451 adults (55% women). Participants mainly consisted of young adults with a mean age of 23.30 years, ranging from 18 to 65 years (SD = 6.97). A mediation model indicated that coronavirus stress had a significant predictive effect on optimism-pessimism, psychological inflexibility, and psychological problems. Further, optimism-pessimism and psychological inflexibility mediated the effect of coronavirus stress on psychological problems in adults. Lastly, optimism-pessimism predicted the psychological problems of adults through psychological inflexibility. These results elucidate our understanding of the role of mediators in coronavirus stress and psychological health problems. The findings are useful in terms of providing evidence for tailoring interventions and implementing preventative approaches to mitigate the psychopathological consequences of COVID-19. Based on the present findings, the potential utility of acceptance and commitment therapy is discussed within the context of COVID-19.

This study systematically reviews randomly selected 155 experimental studies in education field originated in the Republic of Turkey between 2010 and 2020. Indiscriminate choice of sample size in recent publications prompted us to evaluate their statistical power and precision. First, above and beyond our review, we could not identify any large-scale experiments such as cluster-randomized or multisite randomized trials, which overcome shortcomings of small-scale experiments, better suit to the organizational structure of the education field, nevertheless require far greater effort and financial resources. Second, none of the small-scale experiments has reported or conducted ex-ante power analysis. Third, results indicate that studies are sufficiently powered to detect medium effects and above (Cohen's d ≥ 0.50), however they are underpowered to detect small effects (Cohen's d ≤ 0.20). Trends in the past ten years indicate precision remained unchanged. We made several recommendations to increase the precision of experimental designs and improve their evidential values: Determine sample size prior to an experiment with power analysis routine, randomize subjects / clusters to obtain unbiased estimates, collect pre-test information and other relevant covariates, adjust for baseline differences beyond covariate control, document attrition, report standardized treatment effect and standardized variance parameters. Findings should be interpreted considering minimum effects in education that are relevant to education policy and practice.

The coronavirus (COVID-19) pandemic is currently a global health threat attributed to negatively affecting the mental health and well-being of people globally. The purpose of the present study is to examine the mediating role of optimism-pessimism and psychological inflexibility in the relationship of coronavirus stress with psychological problems among Turkish adults. The sample of the study included 451 adults (55% women). Participants mainly consisted of young adults with a mean age of 23.30 years, ranging from 18 to 65 years (SD= 6.97). A mediation model indicated that coronavirus stress had a significant predictive effect on optimism-pessimism, psychological inflexibility, and psychological problems. Further, optimism-pessimism and psychological inflexibility mediated the effect of coronavirus stress on psychological problems in adults. Lastly, optimism-pessimism predicted the psychological problems of adults through psychological inflexibility. These results elucidate our understanding of the role of mediators in coronavirus stress and psychological health problems. The findings are useful in terms of providing evidence for tailoring interventions and implementing preventative approaches to mitigate the psychopathological consequences of COVID-19. Based on the present findings, the potential utility of Acceptance and Commitment Therapy is discussed within the context of COVID-19.

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A review of literature covering the past decade indicates a shortage of cluster-randomized trials (CRTs) in education and psychology in Turkey, the gold standard that is capable of producing high-quality evidence for high-stake decision making when individual randomization is not feasible. Scarcity of CRTs is not only detrimental to collective knowledge on the effectiveness of interventions but also hinders efficient design of such studies as prior information is at best incomplete or unavailable. In this illustration, we demonstrate how to estimate variance parameters from existing data and transform them into standardized forms so that they can be used in planning sufficiently powered CRTs. The illustration uses publicly available software and guides researchers step by step via introducing statistical models, defining parameters, relating them to notations in statistical models and power formulas, and estimating variance parameters. Finally, we provide example statistical power and minimum required sample size calculations.