• The Korean Journal of Applied Statistics
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• v.36 no.4
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• pp.323-335
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• 2023

In causal analysis of high dimensional data, it is important to reduce the dimension of covariates and transform them appropriately to control confounders that affect treatment and potential outcomes. The augmented inverse probability weighting (AIPW) method is mainly used for estimation of average treatment effect (ATE). AIPW estimator can be obtained by using estimated propensity score and outcome model. ATE estimator can be inconsistent or have large asymptotic variance when using estimated propensity score and outcome model obtained by parametric methods that includes all covariates, especially for high dimensional data. For this reason, an ATE estimation using an appropriate dimension reduction method and semiparametric model for high dimensional data is attracting attention. Semiparametric method or sparse sufficient dimensionality reduction method can be uesd for dimension reduction for the estimation of propensity score and outcome model. Recently, another method has been proposed that does not use propensity score and outcome regression. After reducing dimension of covariates, ATE estimation can be performed using matching. Among the studies on ATE estimation methods for high dimensional data, four recently proposed studies will be introduced, and how to interpret the estimated ATE will be discussed.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.50 no.2
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• pp.86-93
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• 2024

Objectives: Orthognathic surgery is a surgical procedure performed by intraoral approach with established and safe techniques; however, excessive blood loss has been reported in rare cases. In response, investigative efforts to identify methods to reduce the amount of blood loss have been made. Among such methods, the administration of tranexamic acid was reported to reduce the amount of intraoperative blood loss. However, few studies to date have reported the effect of tranexamic acid in orthognathic surgery under hypotensive anesthesia. The present study aimed to investigate the effect of the administration of tranexamic acid on intraoperative blood loss in patients undergoing bimaxillary (maxillary and mandibular) orthognathic surgery under hypotensive anesthesia. Patients and Methods: A total of 156 patients (mean age, 27.0±10.8 years) who underwent bimaxillary orthognathic surgery under hypotensive anesthesia performed by the same surgeon between June 2013 and February 2022 were included in this study. The following data were collected from the medical records of each patient: background factors (age, sex, and body mass index), use of tranexamic acid, surgical procedures, previous medical history, duration of surgery, American Society of Anesthesiology physical status findings before surgery, intraoperative blood loss as a primary outcome, in-out balance, and blood test results. Descriptive statistics were calculated for statistical analysis, and a t-test and the chi-squared test were used for between-group comparisons. Group comparisons were performed after 1:1 propensity score matching to adjust for confounding factors. Statistical significance was set at P<0.05. Results: Comparison between the groups based on the use of tranexamic acid revealed a significant difference in operation time. Propensity score matching analysis revealed that intraoperative blood loss was significantly lower in the tranexamic acid group. Conclusion: The administration of tranexamic acid was effective in reducing intraoperative blood loss in patients undergoing bimaxillary orthognathic surgery under hypotensive anesthesia.

• The Korean Journal of Health Service Management
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• v.11 no.1
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• pp.91-105
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• 2017

Objectives : This study analyzed the differences in length of stay(LoS), total hospital charges(THC), and cost of rehabilitation(CoR) between two types of stroke patients, intracerebral hemorrhage(ICH) and cerebral infarction(CI). Factors associated with these differences were also assessed. Methods : Data were obtained from the 2011 National Inpatient Sample data of Health Insurance Review and Assessment Service. We used propensity score matching to match the characteristics of the two types of stroke patients, and conducted a regression analysis to analyze their associations. Results : The differences between THC, LoS, and CoR by stroke and hospital types were shown. Each type of hospital showed different results. Conclusions : A rapidly aging population will accelerate the number of stroke patients requiring effective management. Studies evaluating healthcare utilization of stroke patients will provide evidence for both healthcare resources allocation and healthcare policy decisions.

• Korea Journal of Hospital Management
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• v.21 no.4
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• pp.45-54
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• 2016

The purpose of this study is to identify patient and hospital characteristics with pulmonary tuberculosis and to analyze factors which were influencing length of stay and treatment. The Korean National Hospital Discharge In-depth Injury Survey database from 2006 to 2012 was used for analysis. Study subjects were 4,704 patients and analyzed by using frequency, chi-square and logistic regression through using STATA 12.0. To avoid selection bias, we used propensity score matching. Analysis results show that the length of stay and treatment of pulmonary tuberculosis was different between insurance types. Patients characteristic(female, comorbidity, admission by outpatient department, medical insurance type) and hospital characteristic(500-999 beds, over 1000 beds) significantly influence length of stay. Admission by outpatient department and over 1000 beds are significantly influence treatment. Based on these findings, it is necessary to clarify between length of stay and treatment outcome by medical aids beneficiaries and audit hospitals follow discharge guidelines in pulmonary tuberculosis patients.

• Journal of Distribution Science
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• v.16 no.1
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• pp.87-99
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• 2018

Purpose - The Export Infrastructure Strengthening Program(EISP) is a project to expand exports of agri-food products through providing customized export information to food distribution companies and supporting overseas information activities. A total of 39.6 billion won was provided by 2016. So, the purpose of this study is to analyze whether EISP is effective for expanding exports of agri-food products. Research design, data, and methodology - A simple average difference between the export performance of the policy beneficiaries and the non-policy beneficiaries can be biased if the export capacity or inherent characteristics of the enterprise are not taken into consideration. In order to solve the problem of such a bias, the propensity score matching(PSM) method has been employed in this study. PSM is a method of converting the characteristics of an export company into an index through logit analysis and then reducing the matching to one dimension to improve the accuracy of the performance measurement. Results - The balancing test was conducted to determine how the characteristics of the policy beneficiary group and the matched policy non-beneficiary group corresponded to each other. As a result of the test, we could not reject the null hypothesis that there was no difference between the two groups, so that after the matching, the two groups were similar and the explanatory variables were well controlled. Using the nearest neighbor matching with propensity score estimating through logit analysis, we estimated average treatment effect on the treated(ATT). The food companies participating the EISP had the effect of increasing the exports of $ 5.88 million. As a result, the number of export contracts increased by 11.77, the number of exporting countries by 7.52, the number of export items by 47.51, and the number of buyers' consultation by 3.50. And overseas marketing expenses increased by 35.92 million won. Except for the number of export contracts, other export performance results showed statistically significant results. Conclusions - As the EISP has a positive effect on the expansion of agro-food exports, efforts should be made to find out the limitations or problems of the policy in the future and to make a greater contribution to the increase of exports.

• Journal of Preventive Medicine and Public Health
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• v.57 no.1
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• pp.1-7
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• 2024

Objectives: Adjusting for potential confounders is crucial for producing valuable evidence in outcome studies. Although numerous studies have been published using the Korea National Health Insurance Claim Database, no study has critically reviewed the methods used to adjust for confounders. This study aimed to review these studies and suggest methods and applications to adjust for confounders. Methods: We conducted a literature search of electronic databases, including PubMed and Embase, from January 1, 2021 to December 31, 2022. In total, 278 studies were retrieved. Eligibility criteria were published in English and outcome studies. A literature search and article screening were independently performed by 2 authors and finally, 173 of 278 studies were included. Results: Thirty-nine studies used matching at the study design stage, and 171 adjusted for confounders using regression analysis or propensity scores at the analysis stage. Of these, 125 conducted regression analyses based on the study questions. Propensity score matching was the most common method involving propensity scores. A total of 171 studies included age and/or sex as confounders. Comorbidities and healthcare utilization, including medications and procedures, were used as confounders in 146 and 82 studies, respectively. Conclusions: This is the first review to address the methods and applications used to adjust for confounders in recently published studies. Our results indicate that all studies adjusted for confounders with appropriate study designs and statistical methodologies; however, a thorough understanding and careful application of confounding variables are required to avoid erroneous results.

• Journal of Yeungnam Medical Science
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• v.34 no.2
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• pp.216-221
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• 2017

Background: This study was conducted to investigate preoperative carcinoembryonic antigen (CEA) as a prognostic factor in colorectal cancer. Methods: Between January 2000 and July 2011, 1298 patients with primary adenocarcinoma colorectal cancer without metastasis, who underwent curative resection were retrospectively identified. The patients were divided into two groups according to serum CEA level at primary diagnosis: a high CEA (HCEA) group (serum CEA ${\geq}6ng/mL$) and a normal CEA (NCEA) group (serum CEA <6 ng/mL). A 1:1 propensity score matching analysis was applied to reduce bias. Finally, 364 patients were enrolled in this study. Matched variables were age, gender, preoperative chemoradiotherapy, tumor site, cell differentiation and pathologic stage. Results: The clinicopathological characteristics of the two groups did not differ significantly difference. The systemic metastasis rate was 16.5% (30/182) and 25.3% (46/182) in the NCEA and HCEA groups, respectively (p=0.039). There were no significant differences in local recurrence or metastatic sites between groups. The 5-year disease-free survival (DFS) rate of the HCEA group was worse than that of the NCEA group; however, there was no significant difference in overall survival between the two groups. Conclusion: Elevated preoperative CEA was related to frequent systemic recurrence and low DFS. Therefore, elevated preoperative CEA could be considered a prognostic factor for worse clinical outcomes in patients with colorectal cancer.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.31 no.4
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• pp.367-377
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• 2021

Objectives: Taxi drivers are exposed to various hazards, such as long periods of sedentary work and traffic-related air pollutants. However, studies on the health effects among taxi drivers in South Korea are insufficient. Methods: To assess subclinical hematologic change related to cardiovascular disease among male taxi drivers, we analyzed data from the second Korean National Environmental Health Survey. Fifty-nine taxi drivers and 1,912 controls were included in the analysis. Propensity score matching was performed to adjust for age, body mass index, and urinary cotinine. A total of 295 subjects were matched with 59 taxi drivers. Leukocyte count, platelet count, hematocrit, triglyceride, total cholesterol, HDL cholesterol land total IgE of the taxi drivers were compared with the control groups. Results: Taxi drivers showed significantly elevated blood leukocytes and platelets. Serum total IgE was significantly reduced in taxi drivers. However, blood leukocytes, platelets, and serum total IgE were not significantly correlated with work period among taxi drivers. Conclusions: Regarding the change of the blood leukocyte count, platelet count, and serum total IgE, taxi driving has the possibility to be associated with peripheral inflammation, humoral immunity and cardiovascular risk.

• Journal of Gastric Cancer
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• v.19 no.2
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• pp.193-201
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• 2019

Purpose: There is no consensus on the optimal method for intracorporeal esophagojejunostomy (EJ) in laparoscopic total gastrectomy (LTG). This study aims to compare 2 established methods of EJ anastomosis in LTG. Materials and Methods: A total of 314 patients diagnosed with gastric cancer that underwent LTG in the period from January 2013 to October 2016 were enrolled in the study. In 254 patients, the circular stapler with purse-string "Lap-Jack" method was used, and in the other 60 patients the linear stapling method was used for EJ anastomosis. After propensity score matching, 58 were matched 1:1, and retrospective data for patient characteristics, surgical outcome, and post-operative complications was reviewed. Results: The 2 groups showed no significant difference in age, body mass index, or other clinicopathological characteristics. After propensity score matching analysis, the linear group had shorter operating time than the circular group ($200.3{\pm}62.0$ vs. $244.0{\pm}65.5$, $P{\leq}0.001$). Early postoperative complications in the circular and linear groups occurred in 12 (20.7%) and 15 (25.9%, P=0.660) patients, respectively. EJ leakage occurred in 3 (5.2%) patients from each group, with 1 patient from each group needing intervention of Clavien-Dindo grade III or more. Late complications were observed in 3 (5.1%) patients from the linear group only, including 1 EJ anastomosis stricture, but there was no statistical significance. Conclusions: Both circular and linear stapling techniques are feasible and safe in performing intracorporeal EJ anastomosis during LTG. The linear group had shorter operative time, but there was no difference in anastomosis complications.

• Physical Therapy Rehabilitation Science
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• v.8 no.2
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• pp.67-73
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• 2019

Objective: The purpose of this study was to compare the differences in the length of hospital stay between hemorrhage stroke survivors with health insurance and those with medical care after controlling all factors except for the type of medical insurance by using the propensity score matching (PSM) method. Design: Retrospective cohort study. Methods: Data from the Korean National Centers for Disease Control and Prevention's In-Depth Discharge Injury Survey between the years 2006 and 2012 were used for analysis. A total of 4,538 cases were defined as persons with hemorrhagic stroke (I60-I62) based on the block of categories in the International Classification of Diseases (10th). In order to analyze the inpatient period differences depending on the type of health care, which reflects one's socio-economic level, the chi-square and t-test was conducted. Results: Frequency and percentage were presented, and regression analysis was used to determine the factors affecting the inpatient period. Age, severity of disease, treatment outcome, and post-discharge status were no longer statistically significant after matching. The inpatient period of the persons receiving medical aid benefits was found to be significantly longer than those with national health insurance (p<0.05). Conclusions: The factors influencing the inpatient period of hemorrhagic stroke survivors were treatment outcomes, severity of disease, hospital admission process, and the type of health care. It is necessary for systematic and comprehensive governmental management for persons with hemorrhagic stroke to be transferred to long-term care facilities.