The purpose of this paper is two-fold. First, it attempts to
estimate the relative wage effect of labor unions in Korea and
second, to analyze the determinants in the decision to join a
union. Through use of the two-step estimation method to adjust
the sample selection bias, the relative wage effect of labor
unions is attained. Using this result, determinants of a worker`s
decision to join a union is estimated for the male production
workers in Korea. After eliminating the sample selection bias,
we estimated that the relative wage effect of labor unions in
Korea to be 2.1%. As for the determinants of a worker`s
decision to join a union, rather than such weak wage effect, the
worker`s decision to join a union, rather than such weak wage
effect, the worker`s socio-economic status plays a greater role.

Ⅰ. Introduction

Ⅱ. The Estimation Model
　1. Determinants of Union Membership
　2. Problems with Sample Selection Bias to Estimate Wage Differential
　3. Estimation Method Using the Three Equation Model

Ⅲ. Estimation Results
　1. Wage Equation After Correcting the Sample Selection Bias
　2. Estimation of Union Membership Structural Form
　3. Relative Wage Effect of Unions

Ⅳ. Conclusion and Policy Implications