A case control study is a type of observational study. In this study design, participants are selected to participate depending on their outcome status. Cases are participants with outcome of interest whereas controls are participants who do not have the outcome of interest. These studies estimate the odds ratio or the odds between the exposure and health outcome, however they cannot prove causality. Advantages of case control studies include the following: inexpensive, easy to design and implement, and are used to study rare outcomes. Case control studies are prone to certain research bias but can be addressed by the investigator through careful designing and planning. This paper describes the case control studies, their advantages, bias in case control studies and how to address them, and discuss the steps in how to conduct this type of study design.

BACKGROUND: Cancer prevention is a crucial challenge in preventive medicine. Several studies have suggested that voluntary health check-ups and recommendations from health professionals are associated with increased participation in cancer screening. In Japan, it is recommended that individuals aged 40-74 years should undergo annual health check-ups; however, the compliance to this recommendation is approximately <50%. According to the national survey, individuals who do not undergo annual health check-ups are at a higher risk for cancer. However, to the best of our knowledge, no previous study has investigated the association between the use of health check-ups and the incidence rate of cancer. We hypothesised that not undergoing periodic health check-ups and/or less use of outpatient medical services are predictors for advanced cancer. METHODS: To explore the relationship between health check-up or outpatient service utilisation and cancer incidence, this retrospective cohort study used data at two time points-baseline in 2014 and endpoint in 2017-from the National Health Insurance (NHI) claims and cancer registry. A multivariable logistic regression analysis was performed to investigate whether cancer diagnosis was associated with health check-up or outpatient service utilisation. RESULTS: A total of 72,171 participants were included in the analysis. The results of the multivariable logistic regression showed that individuals who skipped health check-ups had a higher risk of cancer diagnosis (odds ratio [OR], 1.21; 95% confidence interval [CI], 1.04-1.40). Moreover, not undergoing health check-ups increased the risk of advanced-stage cancer (OR, 1.78; 95% CI, 1.29-2.44). Furthermore, increased rate of outpatient service utilisation was negatively associated with advanced cancer diagnosis. CONCLUSIONS This is the first study reporting that not undergoing health check-ups is a predictor of cancer diagnosis and advanced cancer stage. Primary prevention strategies for NHI members who do not undergo health check-ups must be reassessed. Moreover, future research should examine secondary prevention strategies, such as health education and recommendations from health professionals to facilitate adequate utilisation of preventive health services.
Adult ; Aged ; Humans ; Logistic Models ; Middle Aged ; Neoplasms/epidemiology* ; Odds Ratio ; Preventive Health Services ; Retrospective Studies

BACKGROUND: Epidemiological evidence for the relationship between education and income and carotid intima-media thickness (CIMT) has been limited and inconsistent. The present cross-sectional study investigated this issue using baseline data from the Aidai Cohort Study. METHODS: Study subjects were 2012 Japanese men and women aged 34-88 years. Right and left CIMT were measured at the common carotid artery using an automated carotid ultrasonography device. Maximum CIMT was defined as the largest CIMT value in either the left or right common carotid artery. Carotid wall thickening was defined as a maximum CIMT value > 1.0 mm. RESULTS: The prevalence of carotid wall thickening was 13.0%. In participants under 60 years of age (n = 703) and in those aged 60 to 69 years (n = 837), neither education nor household income was associated with carotid wall thickening or with maximum CIMT. Among those aged 70 years or older (n = 472), however, higher educational level, but not household income, was independently related to a lower prevalence of carotid wall thickening: the multivariate-adjusted odds ratio for high vs. low educational level was 0.43 (95% confidence interval 0.21-0.83, p for trend = 0.01). A significant inverse association was observed between education, but not household income, and maximum CIMT (p for trend = 0.006). CONCLUSIONS Higher educational level may be associated with a lower prevalence of carotid wall thickening and a decrease in maximum CIMT only in participants aged 70 years or older.
Adult ; Aged ; Aged, 80 and over ; Carotid Intima-Media Thickness ; Cohort Studies ; Cross-Sectional Studies ; Educational Status ; Female ; Humans ; Income ; Japan/epidemiology* ; Male ; Middle Aged ; Odds Ratio ; Prevalence

BACKGROUND: Unawareness of stroke symptoms and low income are two barriers that affect the seeking of emergency medical service (EMS). This study aimed to assess the effect of unawareness and low income on seeking EMS and to investigate the regional distribution of the unawareness and low-income status and their associations with failing to call EMS in China. METHODS: A total of 187,723 samples from the China National Stroke Screening Survey was interviewed cross-sectionally. Four status of awareness and annual income were identified: unaware and low-income, unaware-only, low-income-only, and aware and regular income. The outcomes were whether they intended to call EMS or not. The regional distribution of each status and their associations with not calling EMS were presented. RESULTS: The status of unaware and low-income, unaware-only, and low-income-only accounted for 6.3% (11,806/187,673), 11.9% (22,241/187,673), and 21.5% (40,289/187,673) of the total sample, respectively. Not calling EMS was significantly associated with the status of unaware and low-income (odds ratio [OR]: 3.21, 95% confidence interval [CI]: 3.07-3.35), unaware-only (OR: 2.38, 95% CI: 2.31-2.46), and low-income-only (OR: 1.67, 95% CI: 1.63-1.71), compared with the aware and regular income status. The Midwest regions had higher percentages of people in the unaware and low-income status; the East, South, and Central had higher percentages of unaware-only status; the North and Northeast regions had a higher percentage of low-income-only status, compared with other regions. CONCLUSION The existence of the regional difference in unawareness and low income justifies the specific stroke education strategies for the targeted regions and population.
China ; Emergency Medical Services ; Humans ; Odds Ratio ; Socioeconomic Factors ; Stroke

Objective: To explore the association between soil selenium levels and the risk of diabetes in Chinese adults aged 35-74 years. Methods: Data for this study were derived from the China Chronic Diseases and Behavioral Risk Factors Surveillance 2010 survey. Selenium concentrations in soil were obtained from the Atlas of Soil Environmental Background Values in China. A two-level binary logistic regression model was used to determine the association between soil selenium concentrations and the risk of diabetes, with participants nested within districts/counties. Results: A total of 69,332 participants aged 35-74 years, from 158 districts/counties were included in the analysis. Concentrations of selenium in soil varied greatly across the 158 districts/counties, with a median concentration of 0.219 mg/kg ( : 0.185-0.248). The results showed that both Quartile 1 (0.119-0.185 mg/kg) and Quartile 4 (0.249-0.344 mg/kg) groups were positively associated with diabetes compared to a soil selenium concentration of 0.186-0.219 mg/kg (Quartile 2), crude odds ratios ( s) (95% ) were 1.227 (1.003-1.502) and 1.280 (1.048-1.563). The values were 0.045 and 0.013, for Quartile 1 and Quartile 4 groups, respectively. After adjusting for all confounding factors of interest, the Quartile 1 group became non-significant, and the Quartile 4 group had an adjusted (95% ) of 1.203 (1.018-1.421) relative to the reference group (Quartile 2), the values was 0.030. No significant results were seen for the Quartile 3 group (0.220-0.248 mg/kg) compared to the reference group. Conclusion Excessive selenium concentrations in soil could increase the risk of diabetes among Chinese adults aged 35-74 years.
Adult ; Aged ; China ; epidemiology ; Diabetes Mellitus ; chemically induced ; epidemiology ; Diet ; Female ; Humans ; Logistic Models ; Male ; Middle Aged ; Odds Ratio ; Risk Factors ; Selenium ; deficiency ; metabolism ; Soil ; chemistry

BACKGROUND AND OBJECTIVES: The relationship between operator volume and outcomes of percutaneous coronary intervention (PCI) in patients with ST-elevation myocardial infarction (STEMI) has not been fully investigated. We aimed to investigate the relationship between operator PCI volume and in-hospital outcomes after primary PCI for STEMI.METHODS: Among the total of 44,967 consecutive cases of PCI enrolled in the Korean nationwide, retrospective registry (K-PCI registry), 8,282 patients treated with PCI for STEMI by 373 operators were analyzed. PCI volumes above the 75th percentile (>30 cases/year), between the 75th and 25th percentile (10–30 cases/year), and below the 25th percentile (<10 cases/year) were defined as high, moderate, and low-volume operators, respectively. In-hospital outcomes including mortality, non-fatal myocardial infarction (MI), stent thrombosis, stroke, and urgent repeat PCI were analyzed.RESULTS: The average number of primary PCI cases performed by 373 operators was 22.2 in a year. In-hospital mortality after PCI for STEMI was 571 cases (6.9%). In-hospital outcomes by operator volume showed no significant differences in the death rate, cardiac death, non-fatal MI, and stent thrombosis. However, the rate of urgent repeat PCI tended to be lower in the high-volume operator (0.6%) than in the moderate-(0.7%)/low-(1.5%) volume operator groups (p=0.095). The adjusted odds ratios for adverse in-hospital outcomes were similar in the 3 groups. Multivariate analysis also showed that operator volume was not a predictor for adverse in-hospital outcomes.CONCLUSIONS: In-hospital outcomes after primary PCI for STEMI were not associated with operator volume in the K-PCI registry.
Cohort Studies ; Death ; Hospital Mortality ; Humans ; Mortality ; Multivariate Analysis ; Myocardial Infarction ; Odds Ratio ; Percutaneous Coronary Intervention ; Retrospective Studies ; Stents ; Stroke ; Thrombosis ; Treatment Outcome

odds ratios (ORs) of participation in DSME decreased in a fully adjusted model. Respondents living in rural areas had lower ORs for attending DSME compared to those living in urban areas [OR, 0.85; 95% confidence interval (CI), 0.80–0.91]. Service/sales workers and mechanical/manual workers had lower ORs for attending DSME (OR, 0.84; 95% CI, 0.71–0.99; and OR, 0.81; 95% CI, 0.69–0.94, respectively) compared to professional/managerial workers. However, in the subgroup of participants receiving education at PHIs, the likelihood of participation in DSME increased as age increased, and respondents living in rural areas had higher ORs compared to those living in urban areas (OR, 1.73; 95% CI, 1.51–1.98).CONCLUSION: Customized DSME programs targeting socioeconomically vulnerable groups, including residential region and reimbursement of DSME by public insurance, are needed to resolve the inequalities in participation in DSME.]]>
Adult ; Diabetes Mellitus ; Education ; Family Characteristics ; Health Surveys ; Humans ; Insurance ; Korea ; Logistic Models ; Odds Ratio ; Public Health ; Self Care ; Social Class ; Socioeconomic Factors ; Surveys and Questionnaires

ratio (NLR), platelet-to-lymphocyte ratio (PLR), platinum-free interval, and survival time were recorded. NLR, PLR, and cancer antigen 125 (CA125) levels were calculated for an optimal cutoff point using receiver operating characteristic curves. The clinicopathological variables were compared using univariate and multivariate analyses to identify independent predictive factors for platinum resistance and poor survival outcomes.RESULTS: The optimal cutoff points for NLR, PLR, and CA125 were 3.38, 210, and 365 IU/L, respectively. Univariate analysis indicated that NLR >3.38, PLR >210, CA125 >365, advanced stage, suboptimal disease, serous type, and ascites were significant predictive factors for platinum resistance. However, only NLR >3.38 and advanced stage were independent predictive factors with an adjusted odds ratio of 1.880 and 3.333, respectively. Regarding factors associated with poor survival outcomes, only PLR >210 and advanced stage were independent factors, with a hazard ratio of 1.578 and 3.994, respectively.CONCLUSION: High NLR and advanced stage were potential independent predictive factors for platinum resistance, whereas high PLR and advanced stage were potential independent predictive factors for poor survival outcomes.]]>
Ascites ; Blood Platelets ; Drug Therapy ; Fallopian Tubes ; Female ; Humans ; Lymphocytes ; Medical Records ; Multivariate Analysis ; Neutrophils ; Odds Ratio ; Ovarian Neoplasms ; Platinum ; Prognosis ; Retrospective Studies ; ROC Curve

odds ratios (ORs) for large for gestational age (LGA) and macrosomia were analyzed.RESULTS: Of the 2,678 patients, the frequency of GDM diagnosed by C-C and IADPSG criteria was 2.6% and 7.5%. ORs (95% confidence intervals [CIs]) for LGA and macrosomia in the group with GDM by IADPSG criteria and non-treated were 2.81 (95% CI, 1.47–5.38) and 2.84 (95% CI, 1.08–7.47). The risk of LGA and macrosomia did not increase in the group with GDM by IADPSG criteria and treated.CONCLUSION: The risk of LGA and macrosomia for mild GDM diagnosed solely by IADPSG criteria depends on whether they are treated or not. Treatment of GDM based on IADPSG criteria reduces the risk of excessive fetal growth.Trial RegistrationClinical Research Information Service Identifier: KCT0000776]]>
Blood Glucose ; Diabetes, Gestational ; Diagnosis ; Female ; Fetal Development ; Gestational Age ; Glucose ; Glucose Tolerance Test ; Humans ; Information Services ; Odds Ratio ; Pregnancy ; Pregnant Women

odds ratio for multiparity, amniotic fluid index (AFI) >14 cm, and HOB >7.8 cm were 10.80 (95% confidence interval [CI], 1.57–74.94), 5.26 (95% CI, 1.06–26.19), and 10.50 (95% CI, 1.03–107.12), respectively. Areas under the curve (AUCs) for AFI, HOB, and parity were 0.66 (95% CI, 0.54–0.78), 0.74 (95% CI, 0.64–0.85), and 0.69 (95% CI, 0.62–0.76), respectively. HOB had the largest AUC, but there were no significant differences among the AUCs of other factors. The cut-off value of HOB was 6 cm.CONCLUSION: This study showed that the AUC of HOB was greater than that of parity and AFI, although it was not statistically significant. As HOB is a noninvasive and comprehensive marker to predict successful ECV, consideration of HOB would be helpful before conducting ECV. Further studies are needed.]]>
Amniotic Fluid ; Area Under Curve ; Breech Presentation ; Buttocks ; Female ; Humans ; Odds Ratio ; Parity ; Pregnancy ; Pregnant Women ; Prospective Studies ; Pubic Symphysis ; Ultrasonography ; Version, Fetal