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

BACKGROUND: Chronic kidney disease (CKD)-mineral and bone disorder (MBD) and fracture risk are both closely related to declining renal function. Controlling hyperphosphatemia with phosphate binders is a basic principle of CKD-MBD treatment. The aim of this study was to identify differences in fracture risk between pre-dialysis CKD patients and end-stage renal disease (ESRD) on dialysis, and to evaluate the effects of phosphate binders on fracture risk in ESRD patients. METHODS: Data from a total of 89,533 CKD patients comprising CKD diagnosis, dialysis, fracture history, and phosphate binder prescription history from 2012 to 2016 were retrieved from the Health Insurance Review and Assessment Service Database. Multivariate Cox regression analyses were performed to identify whether dialysis or phosphate binders were associated with an increased fracture risk. RESULTS: Overall, the rate of fractures in pre-dialysis CKD patients was 74 per 1,000 patient-years, while that in dialysis patients was 84 per 1,000 patient-years. The risk of fracture in ESRD patients was higher than pre-dialysis CKD patients (hazard ratio, 1.16; 95% confidence interval, 1.12–1.21; P < 0.001) after adjusting for confounding variables. In addition, the fracture risk in patients who were not taking phosphate binders was 20.0% higher compared to ESRD patients taking phosphate binders. CONCLUSION: Fractures were more prevalent in ESRD patients on dialysis than pre-dialysis CKD patients. Use of phosphate binders was associated with a lower fracture risk in ESRD patients.
Cohort Studies ; Confounding Factors (Epidemiology) ; Diagnosis ; Dialysis ; Humans ; Hyperphosphatemia ; Insurance, Health ; Kidney Failure, Chronic ; Prescriptions ; Renal Insufficiency, Chronic

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

OBJECTIVES: The purpose of this study was to investigate the association between the components of metabolic syndrome (MetS) (waist circumference, hyperglycemia, hypertriglyceridemia, low levels of high-density lipoprotein cholesterol, and hypertension) and periodontitis in Korean adults aged 35–79 years. METHODS: In this study, data from the Sixth Korean National Health and Nutrition Examination Survey (KNHANES, 2013–2015) were analyzed. Among the 22,948 participants of the Sixth KNHANES, 8,314 participants, who were aged 35–79 years and had completed all systemic and oral health examinations and questionnaires, were included in this study. Confounding variables associated with the demographics and socioeconomic status and systemic and oral health-related behaviors were age, gender, household income, the educational level, smoking and drinking habits, the physical activity status, and frequency of daily toothbrushing. The independent variables were components of MetS, and the dependent variable was periodontitis. RESULTS: Periodontitis was diagnosed in 37.0% of the participants. The incidence of periodontitis among participants with MetS was 47.9%. The incidences of periodontitis among participants with three, four, and five components of MetS were 44.8%, 50.0%, and 56.2%, respectively. The odds ratio (OR) for periodontitis among participants with MetS was 1.43 (95% confidence interval [CI]: 1.27–1.61). The participants with three, four, and five components of MetS showed a significantly higher OR for periodontitis than those with no components of MetS (three components, OR=1.18, 95% CI: 1.02–1.36; four components, OR=1.34, 95% CI: 1.14–1.59; five components, OR=1.68, 95% CI: 1.29–2.20). CONCLUSIONS: A higher number of components of MetS augments the OR of periodontitis.
Adult ; Cholesterol ; Confounding Factors (Epidemiology) ; Demography ; Drinking ; Epidemiology ; Family Characteristics ; Humans ; Hyperglycemia ; Hypertriglyceridemia ; Incidence ; Lipoproteins ; Motor Activity ; Nutrition Surveys ; Odds Ratio ; Oral Health ; Periodontitis ; Smoke ; Smoking ; Social Class ; Toothbrushing

PURPOSE: This study examined the changes in the nutrient intake and the prevalences of obesity and metabolic syndrome according to the eating alone behavior in middle-aged men and women. METHODS: The data from the 2013 ~ 2017 Korean National Health and Nutrition Examination Survey were analyzed. A total of 7,728 adults (3,404 male, 4,324 female) aged 40 ~ 64 years old were included. The subjects were classified into three groups according to the number of times eating alone per day (0, 1 ~ 2, and 3 times/day). Dietary data were collected by a 1-day 24-h recall. The nutrient intakes were compared among the three groups. Survey logistic regression analyses were conducted to examine the association of the eating alone behavior with obesity and metabolic syndrome, adjusting for the related confounding variables. RESULTS: In men, eating alone was associated significantly with a lower intake of potassium (p-for-trend = 0.048) and lower intake of calories from protein (p-for-trend = 0.04). In women, the proportion of subjects consuming energy less than 75% of the estimated energy requirement (p = 0.001) and less than the estimated adequate requirement of riboflavin (p < 0.001) differed significantly according to the eating alone behavior. The eating alone behavior was positively associated with an increased risk of developing metabolic syndrome (p-for-trend = 0.033), increased blood pressure (p-for-trend < 0.001), and increased waist circumference (p-for-trend = 0.004). On the other hand, in women, however, the eating alone behavior was associated with a decreased risks of developing obesity (p-for-trend = 0.02). No association was found between the eating alone behavior and the risk of metabolic syndrome in women. CONCLUSION: These results suggest that the eating alone behavior is a risk factor for the development of metabolic syndrome in middle-aged Korean men.
Adult ; Blood Pressure ; Confounding Factors (Epidemiology) ; Eating ; Female ; Hand ; Humans ; Logistic Models ; Male ; Nutrition Surveys ; Obesity ; Potassium ; Prevalence ; Riboflavin ; Risk Factors ; Waist Circumference

BACKGROUND: Several studies have suggested that breastfeeding has a positive effect on long-term obesity, diabetes, hypertension, and hyperlipidemia. This study aimed to examine maternal bone health, muscle mass, and obesity based on breastfeeding duration. METHODS: This study was based on the Korea National Health and Nutrition Examination Survey 2010–2011. We selected 2,027 elderly women by screening survey participants with a history of delivery. Multivariate logistic regression analyses were performed to estimate the odds ratios (ORs) of sarcopenia, osteoporosis, and obesity among four breastfeeding groups. RESULTS: The OR of sarcopenia significantly decreased with increasing breastfeeding duration (OR, 0.27; 95% confidence interval [CI], 0.11–0.65; P for trend <0.001), whereas the OR of obesity significantly increased with increasing breastfeeding duration (OR, 2.56; 95% CI, 1.43–4.60; P for trend=0.009) after adjusting for potential confounding variables. We also found a positive correlation between the duration since last delivery and sarcopenia. CONCLUSION: Our results suggest a negative correlation between prolonged breastfeeding and the prevalence of sarcopenia, and a positive correlation between prolonged breastfeeding and the prevalence of obesity. Further studies are needed to clarify the relationship between breastfeeding and sarcopenia in the future.
Aged ; Breast Feeding ; Confounding Factors (Epidemiology) ; Cross-Sectional Studies ; Female ; Humans ; Hyperlipidemias ; Hypertension ; Korea ; Logistic Models ; Mass Screening ; Nutrition Surveys ; Obesity ; Odds Ratio ; Osteoporosis ; Prevalence ; Sarcopenia

BACKGROUND: Cigarette smoking increases the risk of atherosclerosis, which often develops as vascular calcification on radiologic examinations. This study evaluated the relationship between smoking-related factors and incidental abdominal aorta calcification (AAC) detected by computed tomography (CT) among middle-aged and elderly men. METHODS: We assessed the abdominal CT findings of 218 men aged 40 to 81 years who underwent health checkups. The associations between smoking factors and AAC were analyzed using logistic regression analysis to adjust for confounding variables such as age, lifestyle factors, and chronic diseases. RESULTS: Adjusting for confounding variables, the risk of AAC was significantly increased in association with smoking for at least 20 years (adjusted odds ratio [AOR], 5.22; 95% confidence interval [CI], 1.82–14.93), smoking 10+ pack-years (10–20 pack-years: AOR, 4.54; 95% CI, 1.07–5.68; >20 pack-years: AOR, 5.28; 95% CI, 2.10–13.31), and a history of smoking (former smoker: AOR, 2.10; 95% CI, 1.07–5.68; current smoker: AOR, 5.05; 95% CI, 2.08–12.26). In terms of the daily smoking amount, even a low smoking level increased the risk of AAC. CONCLUSION: These findings suggest that smoking for 20+ years, smoking 10+ pack-years, and even a low level of smoking daily increases the likelihood of developing AAC. Clinicians should recommend that patients quit smoking and stress the importance of smoking duration when promoting health in middle-aged and elderly patients.
Aged ; Aorta, Abdominal ; Atherosclerosis ; Chronic Disease ; Confounding Factors (Epidemiology) ; Humans ; Life Style ; Logistic Models ; Male ; Odds Ratio ; Smoke ; Smoking ; Tomography, X-Ray Computed ; Vascular Calcification

BACKGROUND: Cancer survivors are at a higher risk of primary cancer recurrence and development of second primary cancer. In both cases, early disease detection is crucial. This cross-sectional study assessed cancer screening participation rates according to cancer history. METHODS: Data were obtained from the 2010–2012 Korea National Health and Nutrition Examination Survey for 12,500 participants. Of these, 624 cancer survivors were enrolled in this study. Sampling weights were applied to maintain the representativeness of the Korean adult population. RESULTS: Overall 2-year cancer screening rates prior to the survey in male and female cancer survivors were 59.9% and 73.7%, respectively, while opportunistic cancer screening rates were 33.5% and 52.1%, respectively. The odds ratios (95% confidence interval) of the overall cancer screening among the cancer survivors, compared to others, were 1.16 (0.79–1.72) in male and 1.78 (1.20–2.63) in female participants, after the adjustment for confounding variables. The odds ratios (95% confidence interval) for opportunistic cancer screening and National Cancer Screening Program among cancer survivors were 1.56 (1.07–2.27) and 0.80 (0.53–1.21) in males and 2.05 (1.46–2.88) and 0.66 (0.46–0.95) in females. CONCLUSION: Female cancer survivors showed a higher rate of overall and opportunistic cancer screening than did the male cancer survivors. Further efforts are required to improve cancer screening among male cancer survivors.
Adult ; Confounding Factors (Epidemiology) ; Cross-Sectional Studies ; Diagnosis ; Early Detection of Cancer ; Female ; Humans ; Korea ; Male ; Mass Screening ; Neoplasms, Second Primary ; Nutrition Surveys ; Odds Ratio ; Recurrence ; Survivors ; Weights and Measures