Abstract:
To compare multiple regression coefficients estimating methods with existence of multicollinearity among independent variables. The estimation methods are Ordinary Least Squares method (OLS), Restricted Least Squares method (RLS), Restricted Ridge Regression method (RRR) and Restricted Liu method (RL) when restrictions are true and restrictions are not true. In case restrictions are not true, error of restrictions is equal to 5%, 10% and 15%, respectively. The Average Mean Square Error (AMSE) was used as the criteria in the project. The distribution of error is normal distribution with mean equal to 0 and standard deviation equal to 1, 3 and 5, respectively. This size of the samples was vary, which composed of 30, 50 and 100 samples. The level of correlations among the independent variables, the case of 3 independent variables could be classified into 3 levels for which low levels equal to (0.1,0.2,0.3), middle levels equal to (0 4,0.5,0.6) and high levels equal to (0.7,0.8,0.9). In the case of 5 independent variables could be classified into 3 levels for which low levels equal to (0.1,0.2,0.3,0.3), middle levels equal to (0.4,0.5,0.6,0.6) and high levels equal to (0.7,0.8,0.9,0.9). The study used the Monte Carlo Simulation method. The experiment was repeated 1,000 times under each situation. The analyzed results of the data were demonstrated as follow. CASE 1: The restrictions are true. In all cases, RRR and RL methods have a smaller AMSE than OLS and RLS method, respectively. RRR method provides the smallest AMSE when the level of correlations is high and also provides the smallest AMSE for all level of correlations and all sample sizes when standard deviation is equal to 5. However, RL method provides the smallest AMSE when the level of correlations is low and middle, except in the case of standard deviation equal to 3, small sample sizes, RRR method provides the smallest AMSE. The AMSE varies with, most to least, respectively, level of correlations, standard deviation and number of independent variables but converses to sample sizes. CASE 2: The restrictions are not true. In all cases, RRR method provides the smallest AMSE, except in the case of standard deviation equal to 1 and error of restrictions equal to 5%, OLS method provides the smallest AMSE when the level of correlations is low or middle and large sample sizes but small sample sizes, RL method provides the smallest AMSE. In addition, when increase error of restrictions, OLS method provides the smallest AMSE for all level of correlations and all sample sizes, except the level of correlations is high and small sample sizes. Moreover, the case OLS method provides the smallest AMSE, the most RLS method has a smaller AMSE than RRR and RL methods when level of correlations is low or middle and large sample sizes. The AMSE varies with, most to least, respectively, error of restrictions, level of correlations, standard deviation and number of independent variables but converses to sample sizes, except error of restrictions does not effect to AMSE of OLS method.