• Title/Summary/Keyword: sample selection bias

Search Result 68, Processing Time 0.027 seconds

A data-adaptive maximum penalized likelihood estimation for the generalized extreme value distribution

  • Lee, Youngsaeng;Shin, Yonggwan;Park, Jeong-Soo
    • Communications for Statistical Applications and Methods
    • /
    • v.24 no.5
    • /
    • pp.493-505
    • /
    • 2017
  • Maximum likelihood estimation (MLE) of the generalized extreme value distribution (GEVD) is known to sometimes over-estimate the positive value of the shape parameter for the small sample size. The maximum penalized likelihood estimation (MPLE) with Beta penalty function was proposed by some researchers to overcome this problem. But the determination of the hyperparameters (HP) in Beta penalty function is still an issue. This paper presents some data adaptive methods to select the HP of Beta penalty function in the MPLE framework. The idea is to let the data tell us what HP to use. For given data, the optimal HP is obtained from the minimum distance between the MLE and MPLE. A bootstrap-based method is also proposed. These methods are compared with existing approaches. The performance evaluation experiments for GEVD by Monte Carlo simulation show that the proposed methods work well for bias and mean squared error. The methods are applied to Blackstone river data and Korean heavy rainfall data to show better performance over MLE, the method of L-moments estimator, and existing MPLEs.

Estimating the Intergenerational Income Mobility in Korea (한국의 세대 간 소득이동성 추정)

  • Yang, Jung-Seung
    • Journal of Labour Economics
    • /
    • v.35 no.2
    • /
    • pp.79-115
    • /
    • 2012
  • In the study, we try to get reliable estimates of intergenerational income mobility in Korea. At first, we show that the low estimates of previous studies are mainly due to sample selection problem. The direct estimations using OLS after correcting this problem show higher values than previous estimates. We also compute the attenuation bias by decomposing the variances of earnings into the variances of permanent and transitory components of earnings by the results of the regression. Additionally, we try to estimate the range of intergenerational mobility by comparing the OLS results with the results of the two samples instrumental variable estimation and the three samples instrumental variable estimation. The results of these estimations are a little higher than or similar to OLS results.

  • PDF

Geographical Mobility of Vocational High School Graduates (지역 산업수요와 지역이동 : 전문고 졸업생의 첫 일자리를 중심으로)

  • Kim, Kyung-Nyun
    • Journal of Labour Economics
    • /
    • v.33 no.2
    • /
    • pp.53-89
    • /
    • 2010
  • Curricula relevant to labor market needs are often designed with the goals of individual employment and regional development at the forefront. This study provided information on regional scope by investigating the extent and determinants of the geographic mobility of vocational high school graduates and the effects of that mobility on first-job wage rates. Geographic mobility was defined as being employed in other provinces in which vocational schools were located. About 38% of graduates were employed in other provinces. Geographic mobility was positively related to gender and human capital such as health, course of study, vocational certificate, and job training. Mobility led to higher wage rates even after controlling for sample selection bias. The implication is that vocational high school curricula which focus excessively on provincial concerns may weaken a workforce's effectiveness.

  • PDF

Job Mobility and Short-run Wage Changes (직장이동의 유형에 따른 단기임금변화)

  • Kim, Hye-Won;Choi, Minsik
    • Journal of Labour Economics
    • /
    • v.31 no.1
    • /
    • pp.29-57
    • /
    • 2008
  • We construct a unique panel data by using Korean Economically Active Population Survey (KEAPS) from 2003 to 2007 to estimate the returns to different types of job mobility among men. By adopting Mincer(1986)'s method, we estimate the wage change to job mobility after controlling the sample selection bias. There are four different types of job mobility that are concerned in the study: (1) voluntary job-to-job changes without experiencing unemployment, (2) voluntary job changes with experiencing unemployment, (3) involuntary job changes due to layoffs, and (4) involuntary job changes due to discharges. Our findings indicate that Korean men who changed jobs without experiencing unemployment realized wage gains of 7% while those who changed jobs through unemployment period lost 10% of their wages. Among those who changed jobs involuntarily and went through unemployment, the workers who discharged from the previous jobs realized substantially greater wage loss.

  • PDF

The Effect of Sagunja Decoction on Functional Dyspepsia - A Systematic Review and Meta-Analysis (기능성 소화불량에 대한 사군자탕의 치료효과 - 체계적 문헌고찰과 메타분석)

  • Kim, Kyong-lim;Je, Yu-ran;Kim, Kyoung-min
    • The Journal of Internal Korean Medicine
    • /
    • v.42 no.3
    • /
    • pp.259-278
    • /
    • 2021
  • Objectives: This study examines the effect of Sagunja-tang on functional dyspepsia (FD) through a systematic review and meta-analysis of a randomized controlled trial (RCT). Methods: A search for RCTs that tested the effect of Sagunja-tang on functional dyspepsia was conducted in Medline, Embase, PubMed, CENTRAL, CiNii, CNKI, NDSL, RISS, OASIS, and KISS databases on November 8, 2020, with no limit on the year of publication. A meta-analysis was performed by synthesizing the findings, including total efficiency, clinical symptom score, myosin light-chain kinase (MLCK) level (pg/mL, and gastric half-emptying time (min). RevMan 5.4.1 software was used for data analysis. The quality of the literature was evaluated using Cochrane's risk of bias (RoB) tool. Results: A total of 14 RCTs met the selection criteria. As a result of the meta-analysis, the treatment group had higher total efficacy and MLCK levels (gastric antrum, jejunum) than the control group, and the clinical symptom score and gastric half-emptying time were lower. However, due to the low quality of the included RCT and the small sample size, the results may be slightly biased.

The Influence of Children's Elementary School Entrance on Working Conditions of Employed Mothers (자녀의 초등학교 입학이 취업모의 근로조건에 미치는 영향)

  • Lee, Jaehee;Kim, Keun Jin
    • The Journal of the Korea Contents Association
    • /
    • v.19 no.12
    • /
    • pp.647-659
    • /
    • 2019
  • The purpose of this study was to investigate the influence of children's elementary school entrance to working conditions of employed mothers. The data from 4th to 8th wave of Panel Study on Korean Children (PSKC) were used for analysis. Specifically, we examined changes in wages, working hours and regular employment of employed mothers after their children entered elementary schools. We adopted Heck selection model for unbalanced panel data after controlling sample selection bias, and compare results of analysis for unbalanced and balanced panel data. The results showed that children's elementary school entrance reduces employed mothers' wage, working hours and regular employment. These results indicate that mother tend to leave regular job and could not entry into decent job when their children are in elementary school.

Efficiency of Variance Estimators for Two-stage PPS Systematic Sampling (2단 크기비례 계통추출법의 분산추정량 효율성 비교)

  • Kim, Young-Won;Kim, Yeny;Han, Hye-Eun;Kwak, Eun-Sun
    • The Korean Journal of Applied Statistics
    • /
    • v.26 no.6
    • /
    • pp.1033-1041
    • /
    • 2013
  • In this paper, we investigate several variance estimators for pps systematic sampling. Unfortunately, there is no unbiased variance estimators for a systematic sample because systematic sampling can be regarded as a random selection of one cluster. This study provides guidance on which variance estimator may be more appropriate than others in several circumstances. We judge the efficiency of variance estimators for systematic sampling based on of their relative biases and relative mean square error. Also, we investigate variance estimation problems for two-stage systematic sampling applied for the Food Raw Material Consumption Survey and the Establishment Labor Force Survey simulation study, in order to consider the popular two-stage pps systematic sample design for establishment and household survey in Korea.

Occupational Labor Market Activities by College Majors: On the Crisis of Science and Engineering Majors (대학졸업자의 전공계열별 직업노동시장 성과: 이공계 위기의 노동시장 원인론을 중심으로)

  • Kim, Chang-Hwan;Kim, Hyung-Seog
    • Korea journal of population studies
    • /
    • v.29 no.3
    • /
    • pp.1-27
    • /
    • 2006
  • Labor market participation and occupational status for workers majoring in(natural) science and engineering are estimated and compared with workers of other majors at three levels: employment, prestigious occupations, and good occupations. For this, we utilized 2% Public Use Sample of 2000 Korea Census. The results of two-stage probit models, which adjust sample selection bias, do not support the argument that graduates of science and engineering majors are relatively disadvantaged. Workers of engineering majors are more likely to have 'good occupations' at their early job careers, but their advantages fade away quickly as they are aging. Especially at their 40s, their probability of having 'good occupations' start to be likely lower than workers of social science majors. This may be due to low human capital accumulation rates at work places along with quickly outdated skills which are acquired in colleges.

Donation Expenses and Corporate Value: A Focus on the Corporate Governance Structure (기부금 지출과 기업 가치: 기업지배구조를 중심으로)

  • Kim, Soo-Jung;Kang, Shin-Ae
    • Journal of Distribution Science
    • /
    • v.12 no.8
    • /
    • pp.113-121
    • /
    • 2014
  • Purpose - Recently, the number of corporations that practice environmental and social responsibility, besides engaging in traditional profit-seeking activities, has been growing steadily, as interest in Corporate Social Responsibility (CSR) is increasing. Recent research on CSR practices has identified the relationship between CSR activities and corporate value as one of the main issues in this respect. Considering that donations constitute a large proportion of a company's charitable activities, we considered the extent of donation expenses as a charitable activity in order to mitigate sample selection bias. Specifically, we analyzed the impact of donation expenses on firm value, while investigating if this impact varied in response to the level of corporate governance of firms. Research design, data, and methodology - We used non-financial firms listed on the Korean Stock Exchange, having their fiscal year end in December, and the sample period was 2006-2013. For the dependent variable, Tobin's q was used as the corporate value, and for the independent variable, donations were measured as the donation-expense-to-sales ratio. Corporate governance scores, as rated by the Korea Corporate Governance Service, were used to measure corporate governance levels because they consider the overall aspects of governance, including ownership structure, the board of directors, and the audit mechanism of individual companies. To examine the impact of donations on a company in relation to the level of corporate governance, we estimated regression models using the interaction terms of the governance dummy and donation variables. Then, we further estimated the regression models of two sub-samples that were classified according to the level of corporate governance. Similar to previous studies, the study uses variables that affect firm value, such as R&D expenditure, advertising expenses, EBITDA, debt-to-equity ratio, sales growth, company age, and company size as control variables. Results - The empirical results show that firm value significantly increased in response to an increase in donation expenses. Upon including the interaction terms of governance level dummy variables and donations, the coefficients of the interaction terms show significant positive values, while those of donation variables show significant negative values. In the strong governance sub-sample, the relationship between the donation expenses and corporate value was statistically positive (+) and significant. However, in the weak governance sub-sample, the relationship between the donation expenses and corporate value was statistically insignificant and negative (-). Conclusions - The empirical results suggest that donation expenses are significantly linked to an enhanced corporate value if firms have a good corporate governance structure. However, if the corporate governance structure is weak, the same relationship is not necessarily observed. The results of this study show that if a firm has high corporate governance, CSR practices enhance the company's reputation such that it has a positive (+) relationship with corporate value. If a firm has weak corporate governance, on the other hand, CSR practices are recognized as an agency cost and do not increase corporate value.

Analysis of Employment Effect on Assistive Technology Program for the Disabled Using Propensity Score Matching (성향점수 매칭을 이용한 보조공학기기 지원사업의 고용효과 분석)

  • Jun, Y.H.;Rhee, K.M.
    • Journal of rehabilitation welfare engineering & assistive technology
    • /
    • v.7 no.2
    • /
    • pp.133-138
    • /
    • 2013
  • This study was aimed to examine effects of the assistive technology program that has purpose to maintain and promote employment of persons with disabilities. An administrative data constructed by the Korea Employment Agency for the Disabled(KEAD) was utilized. Propensity score matching were used as analysis methods to minish sample selection bias caused by nonrandom sampling. As a result, turnover rate of people with disabilities who used assistive technology device was lower compared to persons with disabilities did not use assistive technology device. Also, in terms of company, for employment promotion effect on the persons with disabilities, company that provided assistive technology device was higher than that of company did not provide assistive technology device. Finally, assistive technology devices were effective in the employment area was confirmed.

  • PDF