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: 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

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

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: A kids café is a popular indoor playground in Korea that combines a playground for young children and a café for their caregivers. There have been no national reports about kids café-related injuries in Korea. This study investigated kids café-related injuries in Korea registered in a multicenter injury surveillance database and analyzed the risk factors for significant kids café-related injuries.METHODS: A multicenter cross-sectional study was performed using the Emergency Department-based Injury In-depth Surveillance registry in Korea between 2011 and 2016. Significant injury was defined as an injury requiring hospitalization or surgery. A multivariable logistic regression model was used to obtain the adjusted odds ratios (aORs) for factors associated with significant kids café-related injuries.RESULTS: Among 1,537,617 injured patients, we extracted 891 patients who were injured in kids cafés. Of these, 46 (5.2%) were admitted, and 39 (4.4%) underwent surgery. The most common injured anatomical site, injury type, and mechanism were lower extremity (28.2%), superficial injury (27.2%), and slip (27.1%), respectively. Among injury-inducing factors, significant injuries were most commonly caused by a trampoline (28.1%), and rock climbing equipment was the only risk factor in a kids café that led to significant injury after adjusting for age, sex, injury mechanism, and injured anatomical sites (aOR, 14.94; 95% confidence interval, 1.51–147.72).CONCLUSION: The rock climbing equipment in a kids café can cause serious injury to children. Establishing safety regulations for rock climbing equipment in kids cafés may have the greatest impact in reducing significant injuries requiring hospitalization or surgery.
Caregivers ; Child ; Cross-Sectional Studies ; Emergencies ; Hospitalization ; Humans ; Korea ; Logistic Models ; Lower Extremity ; Odds Ratio ; Play and Playthings ; Risk Factors ; Social Control, Formal ; Wounds and Injuries

BACKGROUND: This study described and analysed the features of powered mobility device (PMD)-related injuries and compared elderly and younger adult injuries.METHODS: Data from Korea Emergency Department-based Injury In-depth Surveillance (EDIIS) database involving eight emergency departments in 2011–2016 were analysed. The inclusion criteria were injuries sustained during the use of PMDs. The variables were compared between adults aged ≥ 65 years and younger adults. Primary and secondary outcomes were severe trauma and poor clinical course accordingly. The logistic regression analysis was used to identify risk factors for study outcomes.RESULTS: A total of 231 adults were enrolled, of whom 150 were ≥ 65 years of age. The total number of PMD-related injuries and the proportion of elderly injured patients increased annually, and most injuries occurred on the roadway and did not involve crash opponents. By multivariate analysis, patients aged ≥ 65 years had a higher injury severity score (adjusted odds ratio [AOR], 2.78; 95% confidence interval [CI], 1.50–5.40) and had a higher incidence of intensive care unit admissions, surgery, and death (AOR, 2.42; 95% CI, 1.16–5.28).CONCLUSION: Given the higher number and severity of injuries sustained among elderly adults ≥ 65 years of age shown in this study, we recommend that safety educations, such as the use of protective equipment and the safe driving on the roadway, are considered for PMD users ≥ 65 years of age.
Adult ; Aged ; Emergencies ; Emergency Service, Hospital ; Epidemiology ; Humans ; Incidence ; Injury Severity Score ; Intensive Care Units ; Korea ; Logistic Models ; Multivariate Analysis ; Odds Ratio ; Risk Factors ; Wheelchairs

BACKGROUND: Elevated blood pressure is a major preventable cause of cardiovascular diseases. Alcohol consumption is a well-known risk factor of elevated blood pressure. The aldehyde dehydrogenase 2 (ALDH2) polymorphism is common in Eastern Asians, and inactive ALDH2 genotypes are associated with both avoiding alcohol consumption and aldehyde accumulation. Therefore, this study assessed the associations between alcohol consumption and hypertension and blood pressure according to the ALDH2 genotypes.METHODS: This study consists of 8,526 participants in the Dong-gu Study. Multivariate logistic regression was used to calculate the odds ratio (OR) according to alcohol consumption after stratifying by gender and ALDH2 genotypes. Multivariate linear regression was performed to estimate the systolic blood pressure (SBP) and diastolic blood pressure (DBP) according to the amount of alcohol consumed.RESULTS: In men, alcohol consumption was positively associated with both SBP and DBP in active ALDH2 carriers, but not in inactive ALDH2 carriers. In active ALDH2 carriers, compared to non-drinkers, the OR of hypertension was 1.16 (95% confidence interval [CI], 0.91–1.49) for < 1 drink/day, and 1.44 (95% CI, 1.15–1.80) for ≥ 1 drink/day in men. With each 1 drink/day increase, SBP and DBP increased by 3 and 1 mmHg in men, respectively. There was no significant association between ALDH2 genotypes and hypertension and blood pressure in women.CONCLUSION: ALDH2 genotype modified the association between alcohol consumption and blood pressure in men. There was a positive relationship between alcohol consumption and blood pressure in active ALDH2 carriers, but no significant relationship in inactive ALDH2 carriers.
Acetaldehyde ; Alcohol Drinking ; Aldehyde Dehydrogenase ; Asian Continental Ancestry Group ; Blood Pressure ; Cardiovascular Diseases ; Cohort Studies ; Female ; Genotype ; Humans ; Hypertension ; Linear Models ; Logistic Models ; Male ; Odds Ratio ; Oxidoreductases ; Risk Factors

OBJECTIVE: To examine time trends in ultrasonography (US)-guided 14-gauge core needle biopsy (CNB) for breast lesions based on the lesion size, Breast Imaging-Reporting and Data System (BI-RADS) category, and pathologic findings.MATERIALS AND METHODS: We retrospectively reviewed consecutive US-guided 14-gauge CNBs performed from January 2005 to December 2016 at our institution. A total of 22,297 breast lesions were included. The total number of biopsies, tumor size (≤ 10 mm to > 40 mm), BI-RADS category (1 to 5), and pathologic findings (benign, high risk, ductal carcinoma in situ [DCIS], invasive cancer) were examined annually, and the malignancy rate was analyzed based on the BI-RADS category.RESULTS: Both the total number of US scans and US-guided CNBs increased while the proportion of US-guided CNBs to the total number of US scans decreased significantly. The number of biopsies classified based on the tumor size, BI-RADS category, and pathologic findings all increased over time, except for BI-RADS categories 1 or 2 and category 3 (odds ratio [OR] = 0.951 per year, 95% confidence interval [CI]: 0.902, 1.002 and odds ratio = 0.979, 95% CI: 0.970, 0.988, respectively). Both the unadjusted and adjusted total malignancy rates and the DCIS rate increased significantly over time. BI-RADS categories 4a, 4b, and 4c showed a significant increasing trend in the total malignancy rate and DCIS rate.CONCLUSION: The malignancy rate in the results of US-guided 14-gauge CNB for breast lesions increased as the total number of biopsies increased from 2005 to 2016. This trend persisted after adjusting for the BI-RADS category.
Biopsy ; Biopsy, Large-Core Needle ; Breast Neoplasms ; Breast ; Carcinoma, Intraductal, Noninfiltrating ; Image-Guided Biopsy ; Information Systems ; Odds Ratio ; Retrospective Studies ; Ultrasonography

BACKGROUND: This study aimed to identify the relationship between exposure to bisphenol A (BPA) and seafood consumption using a nationally representative data of the general Korean population.METHODS: This study was conducted on 5,402 adults aged 19 years and older (2,488 men, 2,914 women) based on the second Korean National Environmental Health Survey (2012–2014). We stratified the data according to gender and analyzed urinary BPA concentrations in terms of sociodemographic characteristics, health behavior, dietary factor, and seafood consumption. In the high and low BPA exposure groups, the odds ratios (ORs) were calculated using logistic regression analysis according to the top 75th percentile concentration.RESULTS: In men, large fish and tuna and other seafood categories had significantly higher ORs before and after adjustment in the group who consumed seafood more than once a week than in the group who rarely consumed seafood, with an adjusted value of 1.97 (95% confidence interval [CI]: 1.12–3.48) and 1.74 (95% CI: 1.10–2.75), respectively. In the shellfish category, the unadjusted OR was 1.61 (95% CI: 1.00–2.59), which was significantly higher in the group who consumed seafood more than once a week than in the group who rarely consumed seafood. However, the OR after adjusting for the variables was not statistically significant. In women, the frequency of seafood consumption and the concentration of urinary BPA were not significantly associated.CONCLUSIONS: BPA concentration was higher in men who frequently consumed large fish and tuna, shellfish and other seafood in this study.
Adult ; Environmental Health ; Female ; Health Behavior ; Humans ; Logistic Models ; Male ; Odds Ratio ; Seafood ; Shellfish ; Tuna