Align node text in tikZ graph

Question

I have the following tikz picture but I can't figure out how to properly align the characters on the left (A,B,C,D,E). I'm pretty sure there's a better way than how I did it with the node labels. Any ideas? I keep getting lost in the pgf tikz documentation and other examples on SE don't seem to have the right solution for me...

Cheers F

\begin{tikzpicture}[scale=.75]
    \coordinate (y) at (0,6);
    \coordinate (x) at (11,0);
    \draw[<->, style=thick] (y) node[above left]{outcomes} -- (0,0) --  (x);

    \filldraw[red] (1,2) circle (5pt);
    \filldraw[red] (1,3) circle (5pt);
    \filldraw[red] (1,4) circle (5pt);

    \filldraw[blue] (2,1) circle (5pt);
    \filldraw[blue] (2,2) circle (5pt);
    \filldraw[blue] (2,3) circle (5pt);
    \filldraw[blue] (2,4) circle (5pt);

    \filldraw[red] (5,2) circle (5pt);
    \filldraw[red] (5,3) circle (5pt);
    \filldraw[red] (5,4) circle (5pt);

    \filldraw[blue] (6,2) circle (5pt);
    \filldraw[blue] (6,4) circle (5pt);

    \filldraw[red] (9,2) circle (5pt);
    \filldraw[red] (9,3) circle (5pt);
    \filldraw[red] (9,4) circle (5pt);

    \filldraw[blue] (10,3) circle (5pt);
    \filldraw[blue] (10,4) circle (5pt);
    \draw
        (0,1) node[left] {E}
        (0,2) node[left] {D}
        (0,3) node[left] {C}
        (0,4) node[left] {B}
        (0,5) node[left] {A}

        (1,0) node[below] {$\theta$}
        (2,0) node[below] {$\theta'_1$}
        (5,0) node[below] {$\theta$}
        (6,0) node[below] {$\theta'_2$}
        (9,0) node[below] {$\theta$}
        (10,0) node[below] {$\theta'_3$}
\end{tikzpicture}

Answer 1

If the question is whether you may make the code shorter and more efficient, the answer is yes.

\documentclass[tikz,border=3mm]{standalone}
\begin{document}
\begin{tikzpicture}[scale=.75,mark size=5pt]
    \coordinate (y) at (0,6);
    \coordinate (x) at (11,0);
    \draw[stealth-stealth, style=thick] (y) node[above left]{outcomes} -- (0,0) --  (x);
    \path[red] plot[only marks,mark=*] coordinates {
        (1,2) (1,3) (1,4) (5,2) (5,3) (5,4) (9,2) (9,3) (9,4)};
    \path[blue] plot[only marks,mark=*] coordinates {
        (2,1) (2,2) (2,3) (2,4) (6,2) (6,4) (10,3) (10,4)};
    \path foreach \X [count=\Y] in {A,...,E}
     {(0,6-\Y) node[left]{\X}}
     foreach \X in {1,2,3}
     {(4*\X-3,0) node[below] {$\theta$}
      (4*\X-2,0) node[below] {$\theta'_\X$}};
\end{tikzpicture}
\end{document}

Obviously one may tune things (arrows.meta etc.), but I feel that you are really looking for pgfplots.

Here is my comment spelled out.

\documentclass[tikz,border=3mm]{standalone}
\begin{document}
\begin{tikzpicture}[scale=.75,mark size=5pt]
    \coordinate (y) at (0,6);
    \coordinate (x) at (11,0);
    \draw[stealth-stealth, style=thick] (y) node[above left]{outcomes} -- (0,0) --  (x);
    \path[red] plot[only marks,mark=*] coordinates {
        (1,2) (1,3) (1,4) (5,2) (5,3) (5,4) (9,2) (9,3) (9,4)};
    \path[blue] plot[only marks,mark=*] coordinates {
        (2,1) (2,2) (2,3) (2,4) (6,2) (6,4) (10,3) (10,4)};
    \path[nodes={text height=1.1em,text depth=0.25ex}] foreach \X [count=\Y] in {A,...,E}
     {(-2em,6-\Y) node[right,align=left]{\X}}
     foreach \X in {1,2,3}
     {(4*\X-3,0) node[below] {$\theta$}
      (4*\X-2,0) node[below] {$\theta'_\X$}};
\end{tikzpicture}
\end{document}