A General Symbol Guide
There are a lot of symbols (often greek letters or ligatures on English letters) used in statistics and econometrics. Luckliy, most of them follow some standard patterns, and are consistent across textbooks and research (note there are exceptions!).
| Greek letters |
\(\beta_0, \beta_1, \sigma, u\) |
True parameters of population |
| Hats |
\(\hat{\beta_0}, \hat{\beta_1}, \hat{\sigma}, \hat{u}\) |
Our statistical estimates of population parameters, from sample data |
| English capital letters |
\(X_1, X_2, Y\) |
(Random) variables in our sample data |
| English lowercase letters |
\(x_{1i}, x_{2i}, y_i\) |
Individual observations of variables in our sample data |
| Modified capital letters |
\(\bar{X}, \bar{Y}\) |
Statistics calculated from our sample data (e.g. sample mean) |
| Bold capital letters |
\(X= \begin{bmatrix} x_1, x_2, \cdots , x_n \\ \end{bmatrix}\) \(\mathbf{\beta} = \begin{bmatrix} \beta_1, \beta_2, \cdots , \beta_k \\ \end{bmatrix}\) |
Vector or matrix |