It is interested in examining treatment effect on a particular category of subjects or in comparing treatment effects among different subgroups as well as overall treatment effect due to heterogeneity of study subjects. Subgroup analyses are exceedingly common, but they are also often misleading. Conclusions based on subgroup analyses can do harm both when a particular category of people is denied effective treatment (a "false-negative" conclusion), and when ineffective or even harmful treatment is given to a subgroup of people (a "false-positive" conclusion). Because of the frequency and the importance of clinical application of subgroup analysis, researchers need to be cautious about doing subgroup analyses. This study presents guidelines to help conducting subgroup analyses correctly.
Population Characteristics

Confounding is the distortion of a disease/exposure association brought about by other factors which are not considered in the study design or the data analysis. These factors are called confounding factors. We should be cautious in data analysis of observational study of association of disease/exposure, since confounding often occurred in observational study. This study examines confounding effect according to data pattern (the ratio of controls to cases, the ratio of exposures to non-exposures for each level of confounding factor), criteria for treating a variable as a confounding variable, and some notes for the analysis in case-control study.
Case-Control Studies* ; Confounding Factors (Epidemiology) ; Observational Study ; Statistics as Topic

Purpose: Here we aimed to examine the association of breastfeeding (BF) with the metabolic syndrome (Mets) and its components among premenopausal parous Korean women. Methods: We conducted a cross-sectional study on 7,116 Korean women by using nationally representa tive data from the Korea National Health and Nutrition Examination Survey, between 2010 and 2016. Mul­tivariate logistic regression analysis was performed for examining the association of BF with Mets and its components. Results: A total 7,116 women were selected for this study. Mets was present in 12.9% of the study parti cipants. The prevalence of Mets in the BF group (12.38%) was lower than that of the non-BF group (14.69 %) (p<0.05). The prevalence of hypertension and hypertriglyceridemia was significantly higher in the non-BF group compared to that of the BF group. For each of Mets components, the total cholestrol level and systolic blood pressure were significantly higher in the non-BF group, compared to those of the BF group (p<0.05). The BF group was associated with a decreased risk of Mets (odds ratio [OR], 0.82; 95% confidence interval [CI], 0.68–0.99). and lower risks of hypo-high-density lipoprotein-cholesterolemia (OR, 0.78; 95% CI, 0.62–0.68), compared to those of the non-BF group. Conclusion BF is an important factor in reducing the risks of Mets. These results provide fundamental evidence for the establishment of policies for promoting BF.

Purpose: We investigated the the effect of wearing a loose mask on tear-film break-up time using cross-sectional and experimental methods. Methods: This was a comparative analysis of non-invasive tear-film break-up time (NIBUT) after wearing no mask, loose mask, and tight mask for 10 minutes each in 60 eyes with or without dry eye syndrome. NIBUT measurements were performed using a keratograph. Results: The NIBUT values were 7.53 ± 0.83 seconds, 6.19 ± 0.78 seconds, and 7.36 ± 0.68 seconds for the no mask, loose mask, and tight mask groups, respectively. There was no significant difference between the no mask and tight mask groups (ρ-value = 0.517), but the loose mask group had a significantly reduced NIBUT compared with the other groups (ρ-value = 0.013 and 0.022, respectively). Conclusions Wearing a loose mask reduced the tear-film break-up time regardless of the presence or absence of dry eyes and may cause or worsen dry eye symptoms.

Background: This study was to identify the factors influencing smartphone dependence among late schoolaged children, focusing on grit and family strengths. Methods: A cross-sectional descriptive study was conducted with 218 children in grades 5 and 6 who were recruited from elementary schools in U and Y cities. The data were collected through self-reported questionnaires, including smartphone dependence, grit, family strengths and general characteristics, for the month of December 2019, just before the novel coronavirus pandemic after obtaining approval from IRB. The collected data were analyzed using multiple regression. Results: Smartphone usage time, the main purpose of smartphone usage (game and social networking), and grit were identified as significant factors of smartphone dependence. This model explained 38% of the total variance showing the variable of grit with the greatest variance. Conclusions A strategy to develop grit is needed to reduce smartphone dependence among late school-age children.

OBJECTIVES: In observational studies, the methods used to measure medication adherence may affect assessments of the clinical outcomes of drug therapy. This study estimated medication adherence to multidrug therapy in patients with hypertension using different measurement methods and compared their impacts on clinical outcomes. METHODS: This was a retrospective cohort study using the Korean National Health Insurance Service–National Sample Cohort database (2006-2015). Adults diagnosed with hypertension who initiated multidrug antihypertensive therapy in the index year 2007 were included. Adherence was defined as over 80% compliance. Adherence to multidrug antihypertensive therapy was measured in 3 ways using the proportion of days covered (PDC) with 2 approaches to the end-date of the study observations: PDC with at least one drug (PDCwith≥1), PDC with a duration weighted mean (PDCwm), and the daily polypharmacy possession ratio (DPPR). The primary clinical outcome was a composite of cardiovascular and cerebrovascular disease-specific hospitalizations or all-cause mortality. RESULTS: In total, 4,226 patients who initiated multidrug therapy for hypertension were identified. The mean adherence according to the predefined measurements varied from 72.7% to 79.8%. Non-adherence was associated with an increased risk of a primary outcome. The hazard ratios (95% confidence intervals, CIs) primary outcomes varied from 1.38 (95% CI, 1.19 to 1.59) to 1.44 (95% CI, 1.25 to 1.67). CONCLUSIONS Non-adherence to multidrug antihypertensive therapy was significantly associated with an increased risk of a primary clinical outcome. Across the varying estimates based on different methods, medication adherence levels were similar. These findings may provide evidence to support decision-making when assessing medication adherence.

Background: The lipophilic yeasts Malassezia spp. are normally resident on the surface of the human body, and often associated with various skin diseases. Of the 18 known Malassezia spp., Malassezia restricta is the most predominantly identified Malassezia sp. found on the human skin. Malassezia possesses a large number of genes encoding lipases to degrade human sebum triglycerides into fatty acids, which are required not only for their growth, but also trigger skin diseases. Previously, we have shown that MrLIP5 (MRET_0930), one of the 12 lipase genes in the genome of M. restricta, and is the most frequently expressed lipase gene in the scalp of patients with dandruff. Objective: In this study, we aimed to analyze the activity, stability, and expression of MrLip5, with particular focus on pH. Methods: We heterologously expressed MrLip5 in Escherichia coli, and purified and analyzed its activity and expression under different pH conditions. Results: We found that MrLip5 was most active and stable and highly expressed under alkaline conditions, which is similar to that of the diseased skin surface. Conclusion Our results suggest that the activity and expression of MrLip5 are pH-dependent, and that this lipase may play an essential role at the M. restricta-host interface during disease progression.

BACKGROUND: Repeated 24 hour recall has been considered as a preferred method for obtaining accurate dietary information while time and cost for coding and data processing have been a major barrier for their use in large studies. This burden can be resolved by automating the interview and data processing. However, there has been no report about a computerized interview system for dietary survey in a free-living population in Korea. METHODS: This study attempts to test the feasibility of a newly-developed web-based dietary assessment program, Diet Evaluation System (DES) for subjects in a mixed region of urban and rural areas via wireless internet. We conducted total of 134 interviews, twice for each of 67 subjects of various age. As another aspect of feasibility, the group discussion among interviewers was done. RESULTS: Success rate of total attempted interviews was about 70%. Major reasons for problem with DES were instability of wireless internet and consequent inefficient booting of laptops in some areas. It took 14 minute 56 seconds on average to complete an interview and data processing conducted automatically. Subjects' age and internet environment influenced the DES interview time. The group discussion revealed that one-stop system with DES is fast and convenient assuming good wireless internet environment. CONCLUSIONS: Web-based dietary assessment was feasible in this community nutrition survey. To confirm the feasibility in large scale, studies with more comprehensive area and subjects are needed with various wireless condition.
Automatic Data Processing ; Clinical Coding ; Diet ; Diet Surveys ; Feasibility Studies ; Internet ; Korea* ; Methods ; Nutrition Surveys*

OBJECTIVES: Although dietary supplements use in Korea has been rapidly increasing and women are more likely to take dietary supplements more than men, only a few studies have been conducted to investigate factors contributing to gender differences in dietary supplement use in the Korean population. The aim of this study is to evaluate the prevalence of dietary supplement use and also identify gender-specific key factors that contribute to it using the data of the 4th KNHANES. METHODS: Subjects were divided into user and non-user groups according to the answer given to the question that asked whether they had used any dietary supplement for more than 2 weeks on a regular basis during the previous year. Factors related to dietary supplement use were examined by general characteristics, health behavior and eating behavior. RESULTS: Prevalence of dietary supplement use was 13.6% for men and 20.6% for women. Users were more likely to be middle-aged, have higher income and education, have a spouse, or reside in dong areas in both men and women. Regarding health behaviors, men with desirable lifestyle behavior were more likely to take dietary supplements, while men who smoked were less likely to take dietary supplements. Regarding disease history, both men and women with a current disease had higher odds of taking supplements. With regard to dietary behavior, frequent eating out and nutrition attitude were associated with higher odds of taking supplements in both men and in women. CONCLUSIONS: Health or dietary behavior related factors that were associated with taking supplements differed by gender. These findings can be useful for planning gender-specific dietary education and health programs.
Dietary Supplements* ; Eating ; Education ; Feeding Behavior ; Female ; Health Behavior ; Humans ; Korea ; Life Style ; Male ; Nutrition Surveys* ; Prevalence ; Smoke ; Spouses

South Korea has the highest reported suicide rate among all countries belonging to the Organization for Economic Cooperation and Development. Nitrogen is a colorless, odorless and nontoxic gas. Nitrogen gas has, however, been recently used as a method of attempted suicide, its nontoxity notwithstanding. We herein report on an unusual case involving a 30-year-old male who presented with symptoms after a suicide attempt by nitrogen inhalation. Diffusion-weighted imaging of his brain was showed curvilinear high signal intensity in the bilateral frontal and right occipital cortices, with subtle low apparent diffusion coefficient value. In addition, T2-weighted images and fluid attenuated inversion recovery images revealed subtle high signal intensity in the bilateral frontal cortices, basal ganglia and occipital cortices with contrast enhancement.
Adult ; Basal Ganglia ; Brain* ; Diffusion ; Frontal Lobe ; Humans ; Inhalation* ; Korea ; Magnetic Resonance Imaging* ; Male ; Methods ; Nitrogen* ; Occipital Lobe ; Organisation for Economic Co-Operation and Development ; Suicide* ; Suicide, Attempted