\documentclass[crop,tikz,convert=pdf2svg]{standalone}

% Tikz settings optimized for causal graphs.
\usetikzlibrary{shapes,decorations,arrows,calc,arrows.meta,fit,positioning}
\tikzset{
    -Latex,auto,node distance =1 cm and 1 cm,semithick ,
    state/.style ={ellipse, draw, minimum width = 0.7 cm},
    point/.style = {circle, draw, inner sep=0.04cm,fill,node contents={}},
    bidirected/.style={Latex-Latex,dashed},
    el/.style = {inner sep=2pt, align=left, sloped}
}

\begin{document}

% The graph
\begin{tikzpicture}[node distance =0.85 cm and 0.85 cm]
    \node (z) [label = below:z, point];
    \node (w) [above = of z,yshift=0.3cm, label = above:w, point];
    \node (x) [label = below:x, below left = of z, point];
    \node (y) [label = below:y, point, below right = of z];
    \path (z) edge node[above, el] {$\lambda_{zw}$} (w);
    \path (z) edge node[above, el] {$\lambda_{zx}$} (x);
    \path (x) edge node[below] {$\lambda_{xy}$} (y);
    \path[bidirected] (z) edge[bend left= 60] node[above, el] {$\epsilon_{zy}$} (y);    
    \path[bidirected] (z) edge[bend right=60] node[above, el] {$\epsilon_{zx}$} (x);
    \path[bidirected] (z) edge[bend left= 60] node[above, el] {$\epsilon_{zw}$} (w);    
    \path[bidirected] (w) edge[bend left= 60] node[above, el] {$\epsilon_{wy}$} (y);    
\end{tikzpicture}
\end{document}