Definition: Simple linear regression
Definition: Let $y$ and $x$ be two $n \times 1$ vectors.
Then, a statement asserting a linear relationship between $x$ and $y$
\[\label{eq:slrmodel} y = \beta_0 + \beta_1 x + \varepsilon \; ,\]together with a statement asserting a normal distribution for $\varepsilon$
\[\label{eq:slrnoise} \varepsilon \sim \mathcal{N}(0, \sigma^2 V)\]is called a univariate simple regression model or simply, “simple linear regression”.

$y$ is called “dependent variable”, “measured data” or “signal”;

$x$ is called “independent variable”, “predictor” or “covariate”;

$V$ is called “covariance matrix” or “covariance structure”;

$\beta_1$ is called “slope of the regression line”;

$\beta_0$ is called “intercept of the regression line”;

$\varepsilon$ is called “noise”, “errors” or “error terms”;

$\sigma^2$ is called “noise variance” or “error variance”;

$n$ is the number of observations.
When the covariance structure $V$ is equal to the $n \times n$ identity matrix, this is called simple linear regression with independent and identically distributed (i.i.d.) observations:
\[\label{eq:mlrnoiseiid} V = I_n \quad \Rightarrow \quad \varepsilon \sim \mathcal{N}(0, \sigma^2 I_n) \quad \Rightarrow \quad \varepsilon_i \overset{\text{i.i.d.}}{\sim} \mathcal{N}(0, \sigma^2) \; .\]In this case, the linear regression model can also be written as
\[\label{eq:slrmodelsum} y_i = \beta_0 + \beta_1 x_i + \varepsilon_i, \; \varepsilon_i \sim \mathcal{N}(0, \sigma^2) \; .\]Otherwise, it is called simple linear regression with correlated observations.
 Wikipedia (2021): "Simple linear regression"; in: Wikipedia, the free encyclopedia, retrieved on 20211027; URL: https://en.wikipedia.org/wiki/Simple_linear_regression#Fitting_the_regression_line.
Metadata: ID: D163  shortcut: slr  author: JoramSoch  date: 20211027, 07:07.