How to Tikz conceptual flow chart gravitationally with squares and arrows?

Question

I want to make a simple conceptual frame work gravitationally where the connections are not curved from the factors to the event, an example in Fig. 1. My motivation of the gravity approach is in the great thread answer How to find y-axis joint similarity in two pictures?, in an analogue to stiching relativistically images by convert -gravity SouthWest -crop ${W1}x${PX}+0+0 "${1}" +repage check1.png. An illustation of some tools needed here is in the thread TikZ: squares and arrows where rotation and simpfications are necessary, but with the application of the gravity approach. I think the Tikz libraries arrows.meta,chains,decorations.pathreplacing are necessary. Pseudocode

• how to have a separate between the initial factors just like in Fig. 1
• start gravitationally arrow from the right-hand-side of the factor text blocks, connect at the center of the image, and then, point to the middle of the event block
• OR a simple method to make a conceptual flow chart in Tikz

Code without any selection of specific Tikz package because I think it should be possible to do with pure tikz

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,chains,decorations.pathreplacing}
\begin{document}
\begin{figure}
\centering
\begin{tikzpicture}
% TODO apply here gravity approach 
% 1. in placing factor boxes at the left-hand-side
% 2. in starting arrows from the central right-hand-side of those boxes, 
% 3. in joining together at the middle of the whole picture at the central left-hand-side of the event text box
\end{tikzpicture}
\caption{Conceptual flow chart.}
\end{figure}
\end{document}

Fig. 1 Example of expected output but use below minimal initial factors to the event (produced by Google Spreadsheet)

Setting

Minimal expected initial factors

• Demographic variables: Age, gender
• Expert variables: ST, blocks

In connection the the event: Arr.

TeXLive: 2016
Engine: XeTeX
OS: Debian 8.7

Answer 1

\documentclass[tikz, border=5mm]{standalone}
\usetikzlibrary{calc, chains, positioning}
\usepackage{lipsum}

\begin{document}
    \begin{tikzpicture}[
    node distance = 4mm and 16mm,
      start chain = going below,
every node/.style = {draw, fill=gray!30,text width=77mm,
                     on chain},
                        ]
\node (a) {\lipsum*[11]};
\node (b) {\lipsum*[11]};
\node (c) {\lipsum*[11]};
\node (d) {\lipsum*[11]};
%
\coordinate[right=of $(b.east)!0.5!(c.east)$] (e);
% or
% \coordinate[right=of $(a.east)!0.5!(d.east)$] (e);
\node (f) [right=of e] {\lipsum*[2]};
\draw   (a) -| (e) 
        (b) -| (e) 
        (c) -| (e) 
        (d) -| (e);
\draw [->] (e) -- (f);
\end{tikzpicture}
\end{document}

Addendum 1: there is many ways to make TikZ image width equal to text width. One of among them is define nodes width dependent on actual \textwidth. For example:

\documentclass{article}
\usepackage[showframe, % show page layout, this option had to be deleted in real document
            margin=25mm]{geometry}
\usepackage{tikz}
\usetikzlibrary{calc, chains, positioning}
\usepackage{lipsum}


\begin{document}
    \begin{figure}
        \centering
    \begin{tikzpicture}[
    node distance = 4mm and 0.1\textwidth,
      start chain = going below,
every node/.style = {draw, fill=gray!30,
                     minimum width=0.4\textwidth,
                     text width =\pgfkeysvalueof{/pgf/minimum width}-2*\pgfkeysvalueof{/pgf/inner xsep},
                     on chain},
                        ]
\node (a) {\lipsum*[11]};
\node (b) {\lipsum*[11]};
\node (c) {\lipsum*[11]};
\node (d) {\lipsum*[11]};
%
\coordinate[right=of $(a.east)!0.5!(d.east)$] (e);
\node (f) [right=of e] {\lipsum*[2]};
\draw   (a) -| (e)
        (b) -| (e)
        (c) -| (e)
        (d) -| (e);
\draw [->] (e) -- (f);
\end{tikzpicture}
    \end{figure}
\end{document}

Addendum 2: "Mirrored" version as requested in the comment below:

\documentclass{article}
\usepackage[showframe, % show page layout, this option had to be deleted in real document
            margin=25mm]{geometry}
\usepackage{tikz}
\usetikzlibrary{calc, chains, positioning}
\usepackage{lipsum}


\begin{document}
    \begin{figure}
        \centering
    \begin{tikzpicture}[
    node distance = 4mm and 0.1\textwidth,
      start chain = going below,
every node/.style = {draw, fill=gray!30,
              minimum width=0.5\textwidth,
              text width =\pgfkeysvalueof{/pgf/minimum width}-2*\pgfkeysvalueof{/pgf/inner xsep},
              on chain},
                        ]
\node (a) {\lipsum*[11]};
\node (b) {\lipsum*[11]};
\node (c) {\lipsum*[11]};
\node (d) {\lipsum*[11]};
%
\coordinate[left=of $(a.west)!0.5!(d.west)$] (e);
\node (f) [minimum width=0.3\textwidth, left=of e] {\lipsum*[11]};
\draw   (a) -| (e)
        (b) -| (e)
        (c) -| (e)
        (d) -| (e);
\draw [->] (e) -- (f);
\end{tikzpicture}
    \end{figure}
\end{document}

Now also the width of nodes are changed (left is narrowed), but the image width is still equal to \textwidth.

Answer 2

So, something like this?

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}
\newcommand\aaa{Text, text, and then some more text which I'll repeat a few times.}
\newcommand\bbb{\aaa{} \aaa{} \aaa}
\begin{document}
\begin{tikzpicture}[
  box/.style={draw,fill=black!30,text width=7cm},
  node distance=5mm]
\node [box] (a) {\bbb};
\node [box,below=of a] (b) {\bbb};
\node [box,below=of b] (c) {\bbb};
\node [box, below=of c] (d) {\bbb};

\draw (a.east) -- ++(1cm,0) coordinate (top);
\draw (b) -- (b-|top);
\draw (c) -- (c-|top);
\draw (d) -| (top) node [pos=0.75,box,text width=3cm,right=1cm] (e) {\aaa};
\draw [<-] (e.west) -- (e.west-|top);
\end{tikzpicture}
\end{document}