• Survey Research
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• v.7 no.2
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• pp.39-52
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• 2006

Most of Korean survey institutions adopt quota sampling for telephone surveys based on region, gender and age-band. In weekdays, it is well blown that there exist substantial differences in day time in-house rate by individual's socio-demographic attributes. So, quota sampling may induce systematic respondent selection bias. To solve the problem, we propose "time-balanced quota sampling" in which interviewer's call time-band is added as an quota variable. Furthermore, we propose "time-balanced quasi-quota sampling" which is derived by partially relaxing evening time quotas in time-balanced quota sampling. We compare the conventional and the newly proposed quota sampling schemes by drawing Monte Carlo samples from the hypothetical population for which the Korea 2004 time use survey data is assumed.

• The Korean Journal of Applied Statistics
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• v.31 no.6
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• pp.733-749
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• 2018

Sample selection arises as a result of the partial observability of the outcome of interest in a study. Heckman introduced a sample selection model to analyze such data and proposed a full maximum likelihood estimation method under the assumption of normality. Recently sample selection models for binomial and Poisson response variables have been proposed. Based on the theory of symmetry-modulated distribution, we extend these to a model for overdispersed count data. This type of data with no sample selection is often modeled using negative binomial distribution. Hence we propose a sample selection model for overdispersed count data using the negative binomial distribution. A real data application is employed. Simulation studies reveal that our estimation method based on profile log-likelihood is stable.

• Communications for Statistical Applications and Methods
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• v.17 no.1
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• pp.55-66
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• 2010

Propensity score adjustment(PSA) has been suggested as approach to adjustment for volunteer internet survey. PSA attempts to decrease the biases arising from noncoverage and nonprobability sampling in volunteer panel internet surveys. Although PSA is an appealing method, its application for internet survey regarding Korea presidential election and its effectiveness is not well investigated. In this study, we compare the Ni Korea internet survey with the telephone survey conducted by MBMR and KBS for 2007 Korean presidential election. The result of study show that the accuracy of internet survey can be improved by using PSA. And it is critical to include covariates that highly related to the voting tendency and the role of nondemographic variables seems important to improving PSA for Korea presidential election prediction.

• The Korean Journal of Applied Statistics
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• v.28 no.6
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• pp.1047-1061
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• 2015

Stratified random sampling is a powerful sampling strategy to reduce variance of the estimators by incorporating useful auxiliary information to stratify the population. Sample allocation is the one of the important decisions in selecting a stratified random sample. There are two common methods, the proportional allocation and Neyman allocation if we could assume data collection cost for different observation units equal. Theoretically, Neyman allocation considering the size and standard deviation of each stratum, is known to be more effective than proportional allocation which incorporates only stratum size information. However, if the information on the standard deviation is inaccurate, the performance of Neyman allocation is in doubt. It has been pointed out that Neyman allocation is not suitable for multi-purpose sample survey that requires the estimation of several characteristics. In addition to sampling error, non-response error is another factor to evaluate sampling strategy that affects the statistical precision of the estimator. We propose new sample allocation methods using the available information about stratum response rates at the designing stage to improve stratified random sampling. The proposed methods are efficient when response rates differ considerably among strata. In particular, the method using population sizes and response rates improves the Neyman allocation in multi-purpose sample survey.

• Korea journal of population studies
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• v.29 no.3
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• pp.1-27
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• 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.

• Journal of Music and Human Behavior
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• v.10 no.2
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• pp.1-33
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• 2013

The aim of this study was to systematically review the latest clinical trials in music medicine and medical music therapy for pediatric patients. Thirteen databases were searched to obtain randomized controlled/crossover design studies published between the year 2000 and 2012 in English language. Out of 1012 articles retrieved in the initial search, fifteen studies were identified based on an exclusion criteria. Overall, selected articles involved children 1 month to 18 years, sample size of 11 to 150, and total participants of 987. Studies were classified and compared as music medicine or music therapy studies through a systematic synthesis assessing general characteristics, methodological quality, measured outcomes, types of interventions and the study results. Seven music medicine and eight music therapy studies measured seven dependent variables using thirty-six different measurement tools with a large heterogeneity in the selection, type, and method of music interventions. Evaluation of the methodological quality revealed that many studies did not provide a full report of the research method, and did not meet some or most methodological standards, such as randomization, allocation concealment, double or partial blinding, and intention to treat analysis. Although overall research results were positive if not significant, poor methodological quality and heterogeneity in design and intervention strategies raise the question of research bias and trustworthiness issues. The systematic review concluded that music may have a valuable clinical effect in addressing the physical and psychosocial needs of hospitalized children, although more rigorous, homogeneous and replicable studies are greatly needed.

• Korea journal of population studies
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• v.26 no.1
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• pp.171-194
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• 2003

The present study investigates the effects of lopsided regional policy and social prejudice on homeownership disparities by household's place of birth of household head in Seoul. The present study utilizes individual household-level census data (2% sample) to evaluate households' residential well-being denoted by homeownership status during the period of 1980-2000. Decomposition techniques based on tenure choice models were used to provide evidences of the home-ownership disparities caused by regional policy and prejudice. We found that households from Gangwon and Honam provinces represent a disproportionately small percentage of homeownership compared with those originated from other provinces. In the statistical analysis, the present study found that having controlled for the factors traditionally thought to influence households' choice of housing tenure, as well as other housing market characteristics in Seoul, place of birth has played a primary role in determining whether or not households become a homeowner. Most strikingly, while most of the disparity in homeownership ratios between households from Youngnam and households from Gangwon in the housing market is due to the endowment differences in human capitals they bring to the market, those between households from Youngnam and households from Honam is largely due to residual differences explained mainly by social discrimination and prejudice against people from Honam. The present study summarized that place of birth has played a primary role in determining whether or not households become a homeowner in Korea. The present study concluded with some policy issues relevant to this study and suggested some future studies.