Isfahan Gastroenterology and Hepatology Research Center, Isfahan University of Medical Sciences, Isfahan 8174673461, Iran.
Colorectal Research Center, Iran University of Medical Sciences, Tehran 1445613131, Iran.
Int J Environ Res Public Health. 2021 Sep 29;18(19):10296. doi: 10.3390/ijerph181910296.
Effect sizes are the most useful quantities for communicating the practical significance of results and helping to facilitate cumulative science. We hypothesize that the selection of the best-fitted controls can significantly affect the estimated effect sizes in case-control studies. Therefore, we decided to exemplify and clarify this effect on effect size using a large data set. The objective of this study was to investigate the association among variables in functional gastrointestinal disorders (FGIDs) and mental health problems, common ailments that reduce the quality of life of a large proportion of the community worldwide.
In this methodological study, we constitute case and control groups in our study framework using the Epidemiology of Psychological, Alimentary Health and Nutrition (SEPAHAN) dataset of 4763 participants. We devised four definitions for control in this extensive database of FGID patients and analyzed the effect of these definitions on the odds ratio (OR): 1. conventional control: without target disorder/syndrome (sample size 4040); 2. without any positive criteria: criterion-free control (sample size 1053); 3. syndrome-free control: without any disorder/syndrome (sample size 847); 4. symptom-free control: without any symptoms (sample size 204). We considered a fixed case group that included 723 patients with a Rome III-based definition of functional dyspepsia. Psychological distress, anxiety, and depression were considered as dependent variables in the analysis. Logistic regression was used for association analysis, and the odds ratio and 95% confidence interval (95%CI) for OR were reported as the effect size.
The estimated ORs indicate that the strength of the association in the first case-control group is the lowest, and the fourth case-control group, including controls with completely asymptomatic people, is the highest. Ascending effect sizes were obtained in the conventional, criterion-free, syndrome-free, and symptom-free control groups. These results are consistent for all three psychological disorders, psychological distress, anxiety, and depression.
This study shows that a precise definition of the control is mandatory in every case-control study and affects the estimated effect size. In clinical settings, the selection of symptomatic controls using the conventional definition could significantly diminish the effect size.
效应大小是用于传达结果的实际意义并帮助促进累积科学的最有用的量。我们假设，最佳拟合对照的选择会显著影响病例对照研究中估计的效应大小。因此，我们决定使用大型数据集来说明和澄清这种对效应大小的影响。本研究的目的是调查功能性胃肠疾病（FGIDs）和心理健康问题之间的变量之间的关联，这些问题是全世界很大一部分人群生活质量降低的常见疾病。
在这项方法学研究中，我们使用 4763 名参与者的心理、消化健康和营养流行病学（SEPAHAN）数据集在我们的研究框架中构成病例和对照组。我们在 FGID 患者的这个广泛数据库中为对照组设计了四个定义，并分析了这些定义对优势比（OR）的影响：1.常规对照：无目标障碍/综合征（样本量 4040）；2.无任何阳性标准：无标准对照（样本量 1053）；3.无综合征对照：无任何障碍/综合征（样本量 847）；4.无症状对照：无任何症状（样本量 204）。我们认为，包括 723 名基于罗马 III 定义的功能性消化不良患者的固定病例组。心理困扰、焦虑和抑郁被视为分析中的因变量。逻辑回归用于关联分析，报告优势比和 95%置信区间（95%CI）的比值比作为效应大小。
估计的 OR 表明，第一组病例对照的关联强度最低，第四组病例对照包括完全无症状的对照，其关联强度最高。在常规、无标准、无综合征和无症状对照组中获得了递增的效应大小。这些结果对于所有三种心理障碍、心理困扰、焦虑和抑郁都是一致的。
本研究表明，在每一项病例对照研究中，精确的对照定义是强制性的，并影响估计的效应大小。在临床环境中，使用常规定义选择有症状的对照会显著降低效应大小。
