Assumptions of the classical Linear Model (Clm) e So far, we know that given the Gauss Markov assumptions, OLS IS BLUE e In order to do classical hypothesis testing we need to add another assumption(beyond the Gauss-Markov assumptions) Assume that u is independent of x,x2…,xk and u is normally distributed with zero mean and variance 0: u- Normal(0, 02) Economics 20- Prof anderson

The Normal Distribution: the distribution of a continuous r.v. whose value depends on a number of factors, yet no single factor dominates the other. 1. Properties of the normal distribution: 1)The normal distribution curve is symmetrical around its mean valueu. 2)The PDF of the distribution is the highest at its mean value but tails off at its extremities

What is Heteroskedasticity Recall the assumption of homoskedastic implied that conditional on the explanator variables the variance of the unobserved error u was constant If this is not true that is if the variance of u is different for different values of thex's. then the errors are heteroskedastic

Definition (1) Econometrics: economic measurement. (2) Econometrics: the social science in which the tools of economic theory, mathematics, and statistical inference are applied to the analysis of economic phenomena. (3) Econometrics: the result of a certain outlook on the role of economics, consists of the application of mathematical statistics to economic data to lend

Time series vs Cross sectional e Time series data has a temporal ordering unlike cross-section data Will need to alter some of our assumptions to take into account that we no longer have a random sample of individuals Instead. we have one realization of a stochastic(i.e. random) process Economics 20- Prof anderson

Testing for AR(IS eria Correlation Want to be able to test for whether the errors are serially correlated or not Want to test the null thatp=0 in u,=pu, 1 +et=2.. where u is the model error

Simultaneity Simultaneity is a specific type of endogeneity problem in which the explanatory variable is jointly determined with the dependent variable 2 As with other types of endogeneity, IV estimation can solve the problem o Some special issues to consider with simultaneous equations modelS(SEM) Economics 20- Prof anderson

一、二元离散选择模型的经济背景 二、二元离散选择模型 三、二元 Probit离散选择模型及其参数估计 四、二元 Logit离散选择模型及其参数估计 五、二元离散选择模型的变量显著性检验

• 一、多重共线性的概念 • 二、实际经济问题中的多重共线性 • 三、多重共线性的后果 • 四、多重共线性的检验 • 五、克服多重共线性的方法 • 六、案例 • *七、分部回归与多重共线性

一、多重共线性 对于模型 在求最小二乘估计时,要求XX的逆存在。当XX的逆不 存在时,即,x之间存在高相关的情况,我们称之为多重 共线性