% Scheme of Covariance
\documentclass[margin=0.5cm]{standalone}
\usepackage{tikz}
\usepackage{amssymb}
\begin{document}
\begin{tikzpicture}
    \usetikzlibrary{positioning}
    \tikzset{
        point/.style = {circle, inner sep={.75\pgflinewidth}, opacity=1, draw, black, fill=black},
        point name/.style = {insert path={coordinate (#1)}},
    }
    \begin{scope}[yshift=0]
        \draw (-4, 0.5) -- (4,0.5) node[right] {$Y_i$};
        \draw (-4, -0.5) -- (4,-0.5) node[right] {$Y_j$};
        \node at (6, 0) {$\mathrm{Cov}(Y_i, Y_j) > 0$};
        \node (EYipoint) at (0,0.5) {$\times$};
        \node at (0, 1) {$\mathbb{E}(Y_i)$};
        \node (EYipoint) at (0,-0.5) {$\times$};
        \node at (0, -1) {$\mathbb{E}(Y_j)$};

        \foreach \x in {-3, 0.5, 2.75} {
            \node[point] at (\x, 0.5) {};
        }
        \foreach \x in {-2, -1, 3} {
            \node[point] at (\x, -0.5) {};
        }
    \end{scope}
    \begin{scope}[yshift=-100]
        \draw (-4,0.5) -- (4,0.5) node[right] {$Y_i$};
        \draw (-4,-0.5) -- (4,-0.5) node[right] {$Y_j$};
        \node at (6, 0) {$\mathrm{Cov}(Y_i, Y_j) \approx 0$};
    \end{scope}

\end{tikzpicture}
\end{document}