Ordinary Least Squares Regression Example
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Least-Squares Fitting of Circles and Ellipses∗
Least-Squares Fitting of Circles and Ellipses∗ Walter Gander Gene H. Golub Rolf Strebel Dedicated to Ake˚ Bj¨orck on the occasion of his 60th birthday. Abstract Fitting circles and ellipses to given points in the plane is a problem that arises in many application areas, e.g. computer graphics [1], coordinate metrol- ogy [2], petroleum engineering [11], statistics [7]. In the past, algorithms have been given which fit circles and ellipses in some least squares sense without minimizing the geometric distance to the given points [1], [6]. In this paper we present several algorithms which compute the ellipse for which the sum of the squares of the distances to the given points is minimal. These algorithms are compared with classical simple and iterative methods. Circles and ellipses may be represented algebraically i.e. by an equation of the form F(x) = 0. If a point is on the curve then its coordinates x are a zero of the function F. Alternatively, curves may be represented in parametric form, which is well suited for minimizing the sum of the squares of the distances. 1 Preliminaries and Introduction Ellipses, for which the sum of the squares of the distances to the given points is minimal will be referred to as \best fit” or \geometric fit", and the algorithms will be called \geometric". Determining the parameters of the algebraic equation F (x)=0intheleast squares sense will be denoted by \algebraic fit" and the algorithms will be called \algebraic". We will use the well known Gauss-Newton method to solve the nonlinear least T squares problem (cf. -
Ordinary Least Squares 1 Ordinary Least Squares
Ordinary least squares 1 Ordinary least squares In statistics, ordinary least squares (OLS) or linear least squares is a method for estimating the unknown parameters in a linear regression model. This method minimizes the sum of squared vertical distances between the observed responses in the dataset and the responses predicted by the linear approximation. The resulting estimator can be expressed by a simple formula, especially in the case of a single regressor on the right-hand side. The OLS estimator is consistent when the regressors are exogenous and there is no Okun's law in macroeconomics states that in an economy the GDP growth should multicollinearity, and optimal in the class of depend linearly on the changes in the unemployment rate. Here the ordinary least squares method is used to construct the regression line describing this law. linear unbiased estimators when the errors are homoscedastic and serially uncorrelated. Under these conditions, the method of OLS provides minimum-variance mean-unbiased estimation when the errors have finite variances. Under the additional assumption that the errors be normally distributed, OLS is the maximum likelihood estimator. OLS is used in economics (econometrics) and electrical engineering (control theory and signal processing), among many areas of application. Linear model Suppose the data consists of n observations { y , x } . Each observation includes a scalar response y and a i i i vector of predictors (or regressors) x . In a linear regression model the response variable is a linear function of the i regressors: where β is a p×1 vector of unknown parameters; ε 's are unobserved scalar random variables (errors) which account i for the discrepancy between the actually observed responses y and the "predicted outcomes" x′ β; and ′ denotes i i matrix transpose, so that x′ β is the dot product between the vectors x and β. -
Lesson 4 – Instrumental Variables
Ph.D. IN ENGINEERING AND Advanced methods for system APPLIED SCIENCES identification Ph.D. course Lesson 4: Instrumental variables TEACHER Mirko Mazzoleni PLACE University of Bergamo Outline 1. Introduction to error-in-variables problems 2. Least Squares revised 3. The instrumental variable method 4. Estimate an ARX model from ARMAX generated data 5. Application study: the VRFT approach for direct data driven control 6. Conclusions 2 /44 Outline 1. Introduction to error-in-variables problems 2. Least Squares revised 3. The instrumental variable method 4. Estimate an ARX model from ARMAX generated data 5. Application study: the VRFT approach for direct data driven control 6. Conclusions 3 /44 Introduction Many different solutions have been presented for system identification of linear dynamic systems from noise-corrupted output measurements On the other hand, estimation of the parameters for linear dynamic systems when also the input is affected by noise is recognized as a more difficult problem Representations where errors or measurement noises are present on both inputs and outputs are usually called Errors-in-Variables (EIV) models In case of static systems, errors-in-variables representations are closely related to other well-known topics such as latent variables models and factor models 4 /44 Introduction Errors-in-variables models can be motivated in several situations: • modeling of the dynamics between the noise-free input and noise-free output. The reason can be to have a better understanding of the underlying relations (e.g. in econometrics), rather than to make a good prediction from noisy data • when the user lacks enough information to classify the available signals into inputs and outputs and prefer to use a “symmetric” system model. -
Ordinary Least Squares: the Univariate Case
Introduction The OLS method The linear causal model A simulation & applications Conclusion and exercises Ordinary Least Squares: the univariate case Clément de Chaisemartin Majeure Economie September 2011 Clément de Chaisemartin Ordinary Least Squares Introduction The OLS method The linear causal model A simulation & applications Conclusion and exercises 1 Introduction 2 The OLS method Objective and principles of OLS Deriving the OLS estimates Do OLS keep their promises ? 3 The linear causal model Assumptions Identification and estimation Limits 4 A simulation & applications OLS do not always yield good estimates... But things can be improved... Empirical applications 5 Conclusion and exercises Clément de Chaisemartin Ordinary Least Squares Introduction The OLS method The linear causal model A simulation & applications Conclusion and exercises Objectives Objective 1 : to make the best possible guess on a variable Y based on X . Find a function of X which yields good predictions for Y . Given cigarette prices, what will be cigarettes sales in September 2010 in France ? Objective 2 : to determine the causal mechanism by which X influences Y . Cetebus paribus type of analysis. Everything else being equal, how a change in X affects Y ? By how much one more year of education increases an individual’s wage ? By how much the hiring of 1 000 more policemen would decrease the crime rate in Paris ? The tool we use = a data set, in which we have the wages and number of years of education of N individuals. Clément de Chaisemartin Ordinary Least Squares Introduction The OLS method The linear causal model A simulation & applications Conclusion and exercises Objective and principles of OLS What we have and what we want For each individual in our data set we observe his wage and his number of years of education. -
Chapter 2: Ordinary Least Squares Regression
Chapter 2: Ordinary Least Squares In this chapter: 1. Running a simple regression for weight/height example (UE 2.1.4) 2. Contents of the EViews equation window 3. Creating a workfile for the demand for beef example (UE, Table 2.2, p. 45) 4. Importing data from a spreadsheet file named Beef 2.xls 5. Using EViews to estimate a multiple regression model of beef demand (UE 2.2.3) 6. Exercises Ordinary Least Squares (OLS) regression is the core of econometric analysis. While it is important to calculate estimated regression coefficients without the aid of a regression program one time in order to better understand how OLS works (see UE, Table 2.1, p.41), easy access to regression programs makes it unnecessary for everyday analysis.1 In this chapter, we will estimate simple and multivariate regression models in order to pinpoint where the regression statistics discussed throughout the text are found in the EViews program output. Begin by opening the EViews program and opening the workfile named htwt1.wf1 (this is the file of student height and weight that was created and saved in Chapter 1). Running a simple regression for weight/height example (UE 2.1.4): Regression estimation in EViews is performed using the equation object. To create an equation object in EViews, follow these steps: Step 1. Open the EViews workfile named htwt1.wf1 by selecting File/Open/Workfile on the main menu bar and click on the file name. Step 2. Select Objects/New Object/Equation from the workfile menu.2 Step 3. -
Time-Series Regression and Generalized Least Squares in R*
Time-Series Regression and Generalized Least Squares in R* An Appendix to An R Companion to Applied Regression, third edition John Fox & Sanford Weisberg last revision: 2018-09-26 Abstract Generalized least-squares (GLS) regression extends ordinary least-squares (OLS) estimation of the normal linear model by providing for possibly unequal error variances and for correlations between different errors. A common application of GLS estimation is to time-series regression, in which it is generally implausible to assume that errors are independent. This appendix to Fox and Weisberg (2019) briefly reviews GLS estimation and demonstrates its application to time-series data using the gls() function in the nlme package, which is part of the standard R distribution. 1 Generalized Least Squares In the standard linear model (for example, in Chapter 4 of the R Companion), E(yjX) = Xβ or, equivalently y = Xβ + " where y is the n×1 response vector; X is an n×k +1 model matrix, typically with an initial column of 1s for the regression constant; β is a k + 1 ×1 vector of regression coefficients to estimate; and " is 2 an n×1 vector of errors. Assuming that " ∼ Nn(0; σ In), or at least that the errors are uncorrelated and equally variable, leads to the familiar ordinary-least-squares (OLS) estimator of β, 0 −1 0 bOLS = (X X) X y with covariance matrix 2 0 −1 Var(bOLS) = σ (X X) More generally, we can assume that " ∼ Nn(0; Σ), where the error covariance matrix Σ is sym- metric and positive-definite. Different diagonal entries in Σ error variances that are not necessarily all equal, while nonzero off-diagonal entries correspond to correlated errors. -
Overview of Total Least Squares Methods
Overview of total least squares methods ,1 2 Ivan Markovsky∗ and Sabine Van Huffel 1 — School of Electronics and Computer Science, University of Southampton, SO17 1BJ, UK, [email protected] 2 — Katholieke Universiteit Leuven, ESAT-SCD/SISTA, Kasteelpark Arenberg 10 B–3001 Leuven, Belgium, [email protected] Abstract We review the development and extensions of the classical total least squares method and describe algorithms for its generalization to weighted and structured approximation problems. In the generic case, the classical total least squares problem has a unique solution, which is given in analytic form in terms of the singular value de- composition of the data matrix. The weighted and structured total least squares problems have no such analytic solution and are currently solved numerically by local optimization methods. We explain how special structure of the weight matrix and the data matrix can be exploited for efficient cost function and first derivative computation. This allows to obtain computationally efficient solution methods. The total least squares family of methods has a wide range of applications in system theory, signal processing, and computer algebra. We describe the applications for deconvolution, linear prediction, and errors-in-variables system identification. Keywords: Total least squares; Orthogonal regression; Errors-in-variables model; Deconvolution; Linear pre- diction; System identification. 1 Introduction The total least squares method was introduced by Golub and Van Loan [25, 27] as a solution technique for an overde- termined system of equations AX B, where A Rm n and B Rm d are the given data and X Rn d is unknown. -
An Analysis of Random Design Linear Regression
An Analysis of Random Design Linear Regression Daniel Hsu1,2, Sham M. Kakade2, and Tong Zhang1 1Department of Statistics, Rutgers University 2Department of Statistics, Wharton School, University of Pennsylvania Abstract The random design setting for linear regression concerns estimators based on a random sam- ple of covariate/response pairs. This work gives explicit bounds on the prediction error for the ordinary least squares estimator and the ridge regression estimator under mild assumptions on the covariate/response distributions. In particular, this work provides sharp results on the \out-of-sample" prediction error, as opposed to the \in-sample" (fixed design) error. Our anal- ysis also explicitly reveals the effect of noise vs. modeling errors. The approach reveals a close connection to the more traditional fixed design setting, and our methods make use of recent ad- vances in concentration inequalities (for vectors and matrices). We also describe an application of our results to fast least squares computations. 1 Introduction In the random design setting for linear regression, one is given pairs (X1;Y1);:::; (Xn;Yn) of co- variates and responses, sampled from a population, where each Xi are random vectors and Yi 2 R. These pairs are hypothesized to have the linear relationship > Yi = Xi β + i for some linear map β, where the i are noise terms. The goal of estimation in this setting is to find coefficients β^ based on these (Xi;Yi) pairs such that the expected prediction error on a new > 2 draw (X; Y ) from the population, measured as E[(X β^ − Y ) ], is as small as possible. -
Chapter 2 Simple Linear Regression Analysis the Simple
Chapter 2 Simple Linear Regression Analysis The simple linear regression model We consider the modelling between the dependent and one independent variable. When there is only one independent variable in the linear regression model, the model is generally termed as a simple linear regression model. When there are more than one independent variables in the model, then the linear model is termed as the multiple linear regression model. The linear model Consider a simple linear regression model yX01 where y is termed as the dependent or study variable and X is termed as the independent or explanatory variable. The terms 0 and 1 are the parameters of the model. The parameter 0 is termed as an intercept term, and the parameter 1 is termed as the slope parameter. These parameters are usually called as regression coefficients. The unobservable error component accounts for the failure of data to lie on the straight line and represents the difference between the true and observed realization of y . There can be several reasons for such difference, e.g., the effect of all deleted variables in the model, variables may be qualitative, inherent randomness in the observations etc. We assume that is observed as independent and identically distributed random variable with mean zero and constant variance 2 . Later, we will additionally assume that is normally distributed. The independent variables are viewed as controlled by the experimenter, so it is considered as non-stochastic whereas y is viewed as a random variable with Ey()01 X and Var() y 2 . Sometimes X can also be a random variable. -
ROBUST LINEAR LEAST SQUARES REGRESSION 3 Bias Term R(F ∗) R(F (Reg)) Has the Order D/N of the Estimation Term (See [3, 6, 10] and References− Within)
The Annals of Statistics 2011, Vol. 39, No. 5, 2766–2794 DOI: 10.1214/11-AOS918 c Institute of Mathematical Statistics, 2011 ROBUST LINEAR LEAST SQUARES REGRESSION By Jean-Yves Audibert and Olivier Catoni Universit´eParis-Est and CNRS/Ecole´ Normale Sup´erieure/INRIA and CNRS/Ecole´ Normale Sup´erieure and INRIA We consider the problem of robustly predicting as well as the best linear combination of d given functions in least squares regres- sion, and variants of this problem including constraints on the pa- rameters of the linear combination. For the ridge estimator and the ordinary least squares estimator, and their variants, we provide new risk bounds of order d/n without logarithmic factor unlike some stan- dard results, where n is the size of the training data. We also provide a new estimator with better deviations in the presence of heavy-tailed noise. It is based on truncating differences of losses in a min–max framework and satisfies a d/n risk bound both in expectation and in deviations. The key common surprising factor of these results is the absence of exponential moment condition on the output distribution while achieving exponential deviations. All risk bounds are obtained through a PAC-Bayesian analysis on truncated differences of losses. Experimental results strongly back up our truncated min–max esti- mator. 1. Introduction. Our statistical task. Let Z1 = (X1,Y1),...,Zn = (Xn,Yn) be n 2 pairs of input–output and assume that each pair has been independently≥ drawn from the same unknown distribution P . Let denote the input space and let the output space be the set of real numbersX R, so that P is a proba- bility distribution on the product space , R. -
Regression Analysis
Regression Analysis Terminology Independent (Exogenous) Variable – Our X value(s), they are variables that are used to explain our y variable. They are not linearly dependent upon other variables in our model to get their value. X1 is not a function of Y nor is it a linear function of any of the other X variables. 2 Note, this does not exclude X2=X1 as another independent variable as X2 and X1 are not linear combinations of each other. Dependent (Endogenous) Variable – Our Y value, it is the value we are trying to explain as, hypothetically, a function of the other variables. Its value is determined by or dependent upon the values of other variables. Error Term – Our ε, they are the portion of the dependent variable that is random, unexplained by any independent variable. Intercept Term – Our α, from the equation of a line, it is the y-value where the best-fit line intercepts the y-axis. It is the estimated value of the dependent variable given the independent variable(s) has(have) a value of zero. Coefficient(s) – Our β(s), this is the number in front of the independent variable(s) in the model below that relates how much a one unit change in the independent variable is estimated to change the value of the dependent variable. Standard Error – This number is an estimate of the standard deviation of the coefficient. Essentially, it measures the variability in our estimate of the coefficient. Lower standard errors lead to more confidence of the estimate because the lower the standard error, the closer to the estimated coefficient is the true coefficient. -
Testing for Heteroskedastic Mixture of Ordinary Least 5
TESTING FOR HETEROSKEDASTIC MIXTURE OF ORDINARY LEAST 5. SQUARES ERRORS Chamil W SENARATHNE1 Wei JIANGUO2 Abstract There is no procedure available in the existing literature to test for heteroskedastic mixture of distributions of residuals drawn from ordinary least squares regressions. This is the first paper that designs a simple test procedure for detecting heteroskedastic mixture of ordinary least squares residuals. The assumption that residuals must be drawn from a homoscedastic mixture of distributions is tested in addition to detecting heteroskedasticity. The test procedure has been designed to account for mixture of distributions properties of the regression residuals when the regressor is drawn with reference to an active market. To retain efficiency of the test, an unbiased maximum likelihood estimator for the true (population) variance was drawn from a log-normal normal family. The results show that there are significant disagreements between the heteroskedasticity detection results of the two auxiliary regression models due to the effect of heteroskedastic mixture of residual distributions. Forecasting exercise shows that there is a significant difference between the two auxiliary regression models in market level regressions than non-market level regressions that supports the new model proposed. Monte Carlo simulation results show significant improvements in the model performance for finite samples with less size distortion. The findings of this study encourage future scholars explore possibility of testing heteroskedastic mixture effect of residuals drawn from multiple regressions and test heteroskedastic mixture in other developed and emerging markets under different market conditions (e.g. crisis) to see the generalisatbility of the model. It also encourages developing other types of tests such as F-test that also suits data generating process.