• 한국벤처창업학회:학술대회논문집
• /
• 2021.11a
• /
• pp.113-117
• /
• 2021

Due to the recent COVID-19 pandemic, SMEs are forced to converge themselves into online business to cope with the rapidly changing business environment. However, due to various difficulties of becoming an online business, most SMEs choose to use services provided by the online sales platform. These platforms offer valuable support such as DSS in return for the high amount of commission fee. We analyze a novel data set from Naver Corporation's 'Smart Store' platform with the quasi-experimental method (propensity score matching technique combined with the difference in differences analysis) to analyze DSS usage and SME's performance empirically. Our results suggest that DSS usage leads to an increase in SME's sales performance in means of sales frequency and sales amount. Additionally, we have found weak support that DSS usage enables SMEs to attract customers better than those not using DSS.

• The Korean Journal of Applied Statistics
• /
• v.36 no.5
• /
• pp.381-397
• /
• 2023

The most representative design used in clinical trials is randomization, which is used to accurately estimate the treatment effect. However, comparison between the treatment group and the control group in an observational study without randomization is biased due to various unadjusted differences, such as characteristics between patients. Propensity score weighting is a widely used method to address these problems and to minimize bias by adjusting those confounding and assess treatment effects. Inverse probability weighting, the most popular method, assigns weights that are proportional to the inverse of the conditional probability of receiving a specific treatment assignment, given observed covariates. However, this method is often suffered by extreme propensity scores, resulting in biased estimates and excessive variance. Several alternative methods including trimming, overlap weights, and matching weights have been proposed to mitigate these issues. In this paper, we conduct a simulation study to compare performance of various propensity score weighting methods under diverse situation, such as limited overlap, misspecified propensity score, and treatment contrary to prediction. From the simulation results overlap weights and matching weights consistently outperform inverse probability weighting and trimming in terms of bias, root mean squared error and coverage probability.

• Journal of the Korean Data and Information Science Society
• /
• v.26 no.6
• /
• pp.1317-1325
• /
• 2015

There are two types of clinical research to figure out risk factor for disease using collected data. One is prospective study to approach the subjects from the present time and the other is retrospective study to find the risk factor using the subject's information in the past. Both approached and study design are different but the purpose of the two studies is to identify a significant difference between two groups and to find out what the variables to influence groups. Especially when comparing the two groups in clinical research, we have to look at the difference between the impact clinical variables by group while controlling the influence of the baseline characteristics variables such as age and sex. However, in the retrospective study, the difference of baseline characteristic variables can occur more frequently because the past records did not randomly assign subjects into two groups. In clinical data analysis use covariates to solve this problem. Typically, the analysis method using the analysis of covariance of variance, adjusted model, and propensity score matching method. This study is introduce the way of equality adjustment between groups data analysis using covariates in retrospective clinical studies and apply it to the recurrence of gastric cancer data.

• The Journal of the Korea Contents Association
• /
• v.17 no.8
• /
• pp.382-395
• /
• 2017

This study tries to analyze whether the Earned Income Tax Credit (EITC), which was modified in 2011, has the effect of work incentive. In this sense, by establishing the 8th Wave of Korea Welfare Panel Study (2013) and the 9th Wave (2014), Furthermore, in order to overcome the methodological limit, the results of two-party analysis method will be compared by firstly carrying out multiple regression analysis and then performing propensity score matching analysis. The 535 households out of 6,025 were selected. The following are the results of multiple digression analysis and propensity score matching analysis. First, there was no statistically meaningful relationship with regard to the perception of the EITC. Second, there was a statistically meaningful result in the reduction of working hours with regard to whether a household received labor incentive or not. The study found that the revised EITC is not providing incentives which stimulates the will to work.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.1
• /
• pp.200-208
• /
• 2009

Trend of R&D expenditure in Korea during the last 10 years, the R&D expenditure has been constantly increasing at an average rate of 10%. The government R&D ekpenditures or subsidies are increasing rapidly But the studies of evaluating impact of government R&D subsidies are few. This study attempts to empirically investigate the effects of government R&D subsidies on private firm's R&D investment in Korean industry by using Propensity score matching method which sign as to whether the relationship between government subsidies and private R&D investments is on stimulating or displacing private R&D expenditures. Empirically, a firm with government R&D subsidy are 733 million dollar more expenditure then don't receive any government R&D funding. Also Government R&D subsidies greatly increase (statistically significant) company financed R&D expenditures only for large firms but had no effect on the R&D expenditures of small & medium sized firms and venture firms.

• Journal of Labour Economics
• /
• v.43 no.3
• /
• pp.33-61
• /
• 2020

The purpose of this study is to analyze the disparity in on-the-job training between regular and non-regular workers and to compare the wage effects of on-the-job training. Using the Korean micro data from the Programme for the International Assessment of Adult Competencies(PIAAC) published by OECD, Propensity Score Method(PSM) is applied to overcome the endogeneity problem. The average treatment effect(ATT) on the training participation is analyzed, using non-regular workers as treatment group and regular workers as comparison group. Odds ratios of non-regular employees' training participation compared to regular employees shows 0.67 times after constructing matching sample and this means that non-regular workers are facing a disadvantageous training opportunity compared to regular workers. In order to estimate the wage effect of on-the-job training, the average treatment effect(ATT) of on-the-job training on average wages for regular workers and non-regular workers is estimated respectively. I find insignificant wage effect from on-the-job training among regular workers and significant positive effect on non-regular worker's wage from on-the-job training.

• The Journal of the Korea Contents Association
• /
• v.19 no.10
• /
• pp.667-676
• /
• 2019

The purpose of this study was to assess the impact of childbirth on socioeconomic status changes of women. Data were collected from Korean Health Panel (2008-2015). A difference-in-differences model with propensity score matching was applied to assess the impact of childbirth on socioeconomic status changes. As a result, variables showing significant differences in the interaction terms indicating the impact of birth were the savings, economic activity, and occupational status. The impact of birth were significant in decreasing the amount of savings and negatively affecting women's economic activities, but in increasing the probability of full-time and regular employees in occupational status. Childbirth appears to have a negative impact on the home economics and socioeconomic status of women. The belief that home economies can be stabilized even after childbirth should be established, and a long-term and sustained support plan should be set up to realize this belief.

• Korea Trade Review
• /
• v.44 no.3
• /
• pp.227-252
• /
• 2019

This study explores the effects of exports on the innovation of Korean firms listed on two Korean stock markets, the Korean Stock Exchange and the Korean Securities Dealers Quotations, between 1999 and 2016. By matching exporting firms to non-exporting ones with propensity score matching, this study accounts for a problem from sample selection bias that may arise from differences in firm-characteristics between the two groups. From the study results, first, both export participation and export volume significantly increase subsequent innovation performance, as measured by the number of patent applications. This result seems to support the "learning by exporting" hypothesis for Korean listed firms. Second, both export participation and export volume narrow innovation scope, proxied as the number of unique International Patent Classification (IPC) codes of the patent applied, the degree to which patents are concentrated in a particular class, and the degree of proximity in the patents. The findings of innovation scope suggest a possible explanation that the learning effect appears in familiar technology fields that firms have previously held, rather than in unfamiliar ones. Third, these results are robust using alternative proxies in the innovation scope, Tobit regressions to consider the non-trivial portion of sample firms with patent applications equal to zeros, and generalized method of moments (GMM) to control for the persistence of innovation measures hearing over years. Finally, the two main results are more pronounced in large firms than in small and medium-sized ones. As for Chaebol firms, however, these results do not appear.

• The Korean Journal of Applied Statistics
• /
• v.30 no.5
• /
• pp.615-632
• /
• 2017

Unlike randomized trial, statistical strategies for inferring the unbiased causal relationship are required in the observational studies. The matching with the propensity score is one of the most popular methods to control the confounders in order to evaluate the effect of the treatment on the outcome variable. Recently, new methods for the causal inference in latent class analysis (LCA) have been proposed to estimate the average causal effect (ACE) of the treatment on the latent discrete variable. They have focused on the application study for the real dataset to estimate the ACE in LCA. In practice, however, the true values of the ACE are not known, and it is difficult to evaluate the performance of the estimated the ACE. In this study, we propose a method to generate a synthetic data using the propensity score in the framework of LCA, where treatment and outcome variables are latent. We then propose a new method for estimating the ACE in LCA and evaluate its performance via simulation studies. Furthermore we present an empirical analysis based on data form the 'National Longitudinal Study of Adolescents Health,' where puberty as a latent treatment and substance use as a latent outcome variable.

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