\documentclass{standalone}

\usepackage{tikz}

\usetikzlibrary{positioning,shapes.arrows, arrows.meta,shapes.geometric}
\begin{document}
\begin{tikzpicture}
    \tikzset{
    every path/.append style = {
            arrows = ->,
            > = stealth,
        },
    every node/.append style = {
            shape = circle,
            draw = black,
            minimum size=3em
        },
    latent/.style = {
            fill = lightgray
        },
    prior/.style = {
            fill = red
        },
    moral/.style = {
    dashed,
    > = {},       % remove arrow tip
    arrows = -,   % ensure no arrows
    }
    }

    \node (y) {$Y$};
    \node[latent] (z) [above left = of y] {$Z$};
    \node[latent] (w) [above right = of y] {$W$};

    \node[latent] (P) [above = of z] {$P$};
    \node[prior] (sigma2) [above = of P] {$\sigma^2$};
    \node[prior] (rho) [above = of w] {$\rho_{1:R}$};
    \node[prior] (alpha) [below = of y] {$\pmb{\alpha}$};

    \path (z) edge (y);
    \path (w) edge (y);
    \path (rho) edge (w);
    \path (alpha) edge (y);
    \path (P) edge (z);
    \path (sigma2) edge (P);

    % moral
    \path[moral] (z) edge (alpha);
    \path[moral] (w) edge (alpha);
    \path[moral] (z) edge (w);

\end{tikzpicture}

\end{document}