Measurement bias (MB) has been described in causal structures but is still not entirely clear. In practice, the correctness of substitution estimate (SE) of effect is a prerequisite for causal inference, usually based on a bidirectionally non-differential misclassification between the measured exposure and the measured outcome. Based on a directed acyclic graph (DAG), this paper proposes a structure for the single-variable measure, where its MB is derived from the choice of an imperfect, "input/output device-like" measurement system. The MB of the SE is influenced both by the measurement system itself and by factors outside the measurement system: while the independence or dependence mechanism of the measurement system still ensures that the MB of the SE is bidirectionally non-differential; however, the misclassification can be bidirectionally non-differential, unidirectionally differential, or bidirectionally differential resulted from the factors outside the measurement system. In addition, reverse causality should be defined at the level of measurement, where measured exposures can influence measured outcomes and vice versa. Combined with temporal relationships, DAGs help elucidate MB's structures, mechanisms, and directionality.
Humans ; Confounding Factors, Epidemiologic ; Data Interpretation, Statistical ; Bias ; Causality

Controlling unmeasured confounders in non-randomized controlled studies is challenging. Negative control theory is based on the theoretical concept that the test result of negative controls must be negative. Setting appropriate negative control incorporates the specificity of association into population studies for the identification and control of unmeasured confounders. This paper explains the principles to control unmeasured confounders using negative control theory from a statistical perspective. A detailed introduction of derived methods based on negative control theory is also introduced, including adjusted standardized mortality ratio method, calibrating P-value method, generalized difference-in-difference model and double negative control method. The reasonable application of those derived methods is also comprehensively summarized based on representative case studies. Negative control is an important statistical design to identify, revise and control unmeasured confounders and a valuable method for comparative effectiveness research based on real-world data.
Humans ; Confounding Factors, Epidemiologic ; Research Design ; Comparative Effectiveness Research ; Bias

confounding variables.RESULTS: The BMD of the total femur and Ward's triangle were significantly different according to the potassium intake among men (P = 0.031 and P = 0.010, respectively). Women in the top tertile for potassium intake showed higher BMD than those in the bottom tertile at all measurement sites (all P < 0.05). Daily potassium intake was significantly related to a decreased risk of osteoporosis at the lumbar spine in postmenopausal women (odds ratios: 0.68, 95% confidence interval: 0.48-0.96, P trend = 0.031). However, the dietary potassium level was not related to the risk of osteoporosis in men.CONCLUSION: Current findings indicate that higher dietary potassium levels have a favorable effect on bone health and preventing osteoporosis in older Korean women.]]>
Absorptiometry, Photon ; Adult ; Bone Density ; Bone Diseases, Metabolic ; Calcium ; Confounding Factors (Epidemiology) ; Cross-Sectional Studies ; Epidemiology ; Female ; Femur ; Femur Neck ; Hip ; Humans ; Logistic Models ; Male ; Methods ; Nutrition Surveys ; Osteoporosis ; Population Surveillance ; Potassium ; Potassium, Dietary ; Prevalence ; Retrospective Studies ; Spine ; Vitamin D

OBJECTIVE: In this study, we evaluated the prevalence of allergic disease in offsprings delivered via the delivery modes of vaginal delivery vs. planned Cesarean section vs. Cesarean section with labor. METHODS: This study included 175 mother-neonate pairs from Severance Hospital who were enrolled in the Cohort for Childhood Origin of Asthma and allergic diseases study. Information regarding prenatal environmental factors, delivery, and diagnosis of allergic diseases was obtained from a questionnaire and medical record review. Patients with at least 3 years of follow-up data were included in this study. Results were adjusted for sex, birth weight, gestational age at birth, season of birth, neonatal intensive care unit admission, parity, breastfeeding, and maternal factors. RESULTS: A total of 175 offsprings were eligible for analysis. Among the subjects, 52.0% were delivered by vaginal delivery, 34.3% by planned Cesarean section, and 16.6% by Cesarean section with labor. Fifty-nine offsprings (33.7%) were diagnosed with allergic disease at a median age of 1 year (range 0.5–3 years). The prevalence of allergic disease was not associated with delivery mode after adjusting for confounding variables. Time period from membrane rupture to delivery, duration of the active phase, and the beginning of the pelvic division prior to Cesarean section were not associated with allergic disease development in offsprings. CONCLUSION: Cesarean section, irrespective of the occurrence of labor before surgery, did not increase the prevalence of allergic disease in infants up to 3 years of age.
Asthma ; Birth Weight ; Breast Feeding ; Cesarean Section* ; Cohort Studies ; Confounding Factors (Epidemiology) ; Diagnosis ; Female ; Follow-Up Studies ; Gestational Age ; Humans ; Infant ; Infant, Newborn ; Intensive Care, Neonatal ; Medical Records ; Membranes ; Parity ; Parturition ; Pregnancy ; Prevalence* ; Rupture ; Seasons

BACKGROUND: This study evaluated the association between nicotine dependence and depressive mood in patients who visited a secondary hospital for smoking cessation treatment.METHODS: From March 2016 to February 2017, a total of 48 patients who visited the smoking cessation clinic of a secondary hospital in Seoul were surveyed through questionnaires. Nicotine dependence was assessed by the Fagerström Test for Nicotine Dependence. The Beck Depression Inventory (BDI) was used to assess depressive mood.RESULTS: The mean BDI score was positively associated with nicotine dependence (P=0.01). In multivariable logistic regression analysis, increasing BDI was associated with higher odds (1.21, 95% confidence interval; 1.02–1.44) of high nicotine dependence after adjusting for all confounding variables.CONCLUSION: Depressive mood was positively associated with nicotine dependence among patients who visited a smoking cessation clinic. Consideration of depressive mood in smoking cessation treatment may be helpful for smoking cessation among patients with a willingness to quit smoking.
Confounding Factors (Epidemiology) ; Depression ; Humans ; Logistic Models ; Nicotine ; Seoul ; Smoke ; Smoking Cessation ; Smoking ; Tobacco Use Disorder

BACKGROUND: The ankle-brachial index (ABI) is a simple, noninvasive clinical test that is useful in the diagnosis of peripheral artery disease (PAD). The borderline ABI value is 0.91–0.99 and has also been reported in endothelial dysfunction and preclinical PAD. We investigated the relationship between resting heart rate as a surrogate marker of autonomic balance and borderline ABI in apparently healthy individuals.METHODS: We evaluated the association between resting heart rate and borderline ABI in 618 participants (348 male and 270 female) in a health examination program. The odds ratios for borderline ABI were calculated using a multivariable logistic regression analysis after adjusting for confounding variables across heart rate quartiles (Q1≤56, Q2=57–62, Q3=63–68, and Q4≥69 beats/min).RESULTS: The overall prevalence of borderline ABI was 13.9%. The age- and sex-adjusted resting heart rate was significantly higher in the borderline ABI group than in the control group (66.9±0.9 vs. 63.0±0.4 beats/min, P < 0.001). The odds ratios (95% confidence intervals) for the borderline ABI in each heart rate quartile were 1.00, 1.04 (0.43–2.52), 1.69 (0.73–3.93), and 3.52 (1.55–7.97) after adjusting for age, sex, smoking status, alcohol intake, regular exercise, body mass index, systolic blood pressure, fasting plasma glucose level, triglyceride level, high-density lipoprotein-cholesterol level, white blood cell count, C-reactive protein level, uric acid level, γ-glutamyltransferase level, hypertension medication, diabetes medication, and dyslipidemia medication.CONCLUSION: These findings indicate that a higher resting heart rate is independently associated with borderline ABI.
Ankle Brachial Index ; Biomarkers ; Blood Glucose ; Blood Pressure ; Body Mass Index ; C-Reactive Protein ; Confounding Factors (Epidemiology) ; Diagnosis ; Dyslipidemias ; Fasting ; Heart Rate ; Heart ; Humans ; Hypertension ; Leukocyte Count ; Logistic Models ; Male ; Odds Ratio ; Peripheral Arterial Disease ; Prevalence ; Smoke ; Smoking ; Triglycerides ; Uric Acid

BACKGROUND: Colon cancer is one of the main causes of mortality. Early adenomatous colon polyp is a precursor of colon cancer through the ‘adenomacarcinoma sequence.’ Epidemiological studies suggest that the neutrophil to lymphocyte ratio can be one of useful inflammatory markers in clinical settings. This study aimed to evaluate the association between neutrophil to lymphocyte ratio and development of early adenomatous colon polyps.METHODS: This cross-sectional study retrospectively examined 960 middle-aged and elderly individuals aged ≥45 years who underwent colonoscopy in a health examination program. Multivariate logistic regression was used to analyze the association between neutrophil to lymphocyte ratio and development of early adenomatous colon polyps.RESULTS: Among the 960 subjects, the prevalence of early adenomatous polyps was 20.7% (n=199). The mean age, body mass index, number of current smokers, white blood cell count, triglyceride level, and number of subjects receiving hypolipidemic drugs were higher in the group with early adenomatous polyps than in the multivariate analysis, the odds ratio (95% confidence interval) for the development of early adenomatous polyps was 1.23 (1.01–1.50) with neutrophil to lymphocyte ratio increment after adjusting the confounding variables (P=0.037).CONCLUSION: We found that the neutrophil to lymphocyte ratio was associated with the development of early adenomatous colon polyps among middle-aged and elderly individuals. Accordingly, this result suggests that regular monitoring of early adenomatous colon polyps may be useful among individuals with a higher neutrophil to lymphocyte ratio.
Adenomatous Polyps ; Aged ; Body Mass Index ; Colon ; Colonic Neoplasms ; Colonic Polyps ; Colonoscopy ; Confounding Factors (Epidemiology) ; Cross-Sectional Studies ; Epidemiologic Studies ; Humans ; Hypolipidemic Agents ; Korea ; Leukocyte Count ; Logistic Models ; Lymphocytes ; Middle Aged ; Mortality ; Multivariate Analysis ; Neutrophils ; Odds Ratio ; Polyps ; Prevalence ; Retrospective Studies ; Triglycerides

BACKGROUND: Several contradictory studies exist on the relationship between raising grandchildren and the grandparent's health. The present study identified the association between raising grandchildren and depression among Korean grandparents.METHODS: The wave 1 (2006) and wave 2 (2008) databases of the Korean longitudinal study on aging (KLoSA) were analyzed. T-test and chi-square test were used to compare the demographics and health condition variable between the two groups based on the presence or absence of raising grandchildren. Logistic regression analysis, including demographics and health conditions, was conducted to identify the relationship between depression and raising grandchildren. Depression was assessed using the Center for Epidemiologic Studies Depression scale (CES-D-10).RESULTS: In all, 4,784 participants (4,636: not raising grandchildren; 148: raising grandchildren) were examined. Significantly lower CES-D-10 scores (3.34 vs. 4.35, P<0.001), and therefore, lower depression (25% vs. 39.9%, P<0.001) was found among grandparents raising grandchildren than those who did not raise grandchildren. After adjusting the confounding variables through logistic regression analysis, the odds ratio of depression when raising grandchildren was 0.57 (95% confidence interval=0.37–0.89), which indicates significant relevance.CONCLUSION: The results show lower depressive symptoms among grandparents raising grandchildren. Even after adjusting the variables, the results presented a lower risk of depression among them.
Adult ; Aging ; Confounding Factors (Epidemiology) ; Demography ; Depression ; Epidemiologic Studies ; Grandparents ; Humans ; Logistic Models ; Longitudinal Studies ; Odds Ratio

PURPOSE: To determine the relationship between uterine leiomyoma and female sexual dysfunction (FSD) among premenopausal and postmenopausal women. MATERIALS AND METHODS: The study population consisted of consecutive women who underwent gynecologic screening tests, including transvaginal ultrasound, and completed the questionnaires on FSD. A total of 841 women were included from January 2010 to December 2011. FSD was defined as Female Sexual Function Index (FSFI) ≤26.55. The relationship between uterine leiomyoma and FSD were compared according to menopausal status. RESULTS: In premenopausal group (n=564), there were no differences in the frequency of FSD (55.0% vs. 58.8%, p=0.387) and total FSFI score. However, in postmenopausal group (n=277), women with uterine leiomyoma had a lower frequency of FSD than those without uterine leiomyoma (71.3% vs. 86.4%, p=0.003). This relationship between uterine leiomyoma and lower frequency of FSD in postmenopausal women remained significant after adjusting for confounding variables. CONCLUSION: The relationship between uterine leiomyoma and FSD is different depending on the menopausal status.
Confounding Factors (Epidemiology) ; Dyspareunia ; Female ; Humans ; Leiomyoma ; Mass Screening ; Menopause ; Sexual Behavior ; Ultrasonography

BACKGROUND: Shift work is associated with a higher risk of cardiovascular diseases. Here, we sought to assess the relationship between shift work and plasma homocysteine levels. Determining the correlations between shift work and homocysteine levels may provide a better understanding of the mechanisms underlying cardiovascular diseases. METHODS: This study was performed using data from routine health examinations of steel workers in 2017. In total, 431 male workers (70 daytime workers and 361 shift workers) employed on a rolling departure schedule were recruited. Plasma homocysteine levels > 15 μmol/L were considered elevated. The χ2, analysis of variance, and multiple logistic regression analyses were used to examine the association between shift work and plasma homocysteine levels. RESULTS: In comparison to daytime workers, the odds ratio (OR) of hyperhomocysteinemia in individuals with < 10 years of shift work was 1.14 (95% confidence interval [CI]: 0.64–2.03), compared to 2.01 (95% CI: 1.14–3.54) for workers with ≥ 10 years of experience. After adjusting for confounding variables, the adjusted OR for shift workers with < 10 years of experience was 0.95 (95% CI: 0.50–1.80), compared to 2.00 (95% CI: 1.07–3.74) for workers with ≥ 10 years of experience. CONCLUSIONS: The risk of hyperhomocysteinemia was significantly higher in shift workers compared to those working normal daytime hours, particularly among long-term shift workers.
Appointments and Schedules ; Cardiovascular Diseases ; Confounding Factors (Epidemiology) ; Homocysteine ; Humans ; Hyperhomocysteinemia ; Logistic Models ; Male ; Odds Ratio ; Plasma ; Steel