\begin
Discover why 18 million people worldwide trust Overleaf with their work.
\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}
\pagestyle{empty}
% Define block styles
\tikzstyle{decision} = [diamond, draw, fill=blue!20,
text width=6em, text badly centered, node distance=3cm, inner sep=0pt]
\tikzstyle{block} = [rectangle, draw, fill=blue!20,
text width=9em, text centered, rounded corners, minimum height=4em]
\tikzstyle{block2} = [rectangle, draw, fill=yellow!20,
text width=9em, text centered, rounded corners, minimum height=4em]
\tikzstyle{line} = [draw, -latex']
\tikzstyle{cloud} = [draw, ellipse,fill=red!20, node distance=3cm,
minimum height=4em]
\begin{figure}[!ht]
\centering
\hspace*{-135pt}
\begin{tikzpicture}[node distance = 2cm, auto]
% nodes
\node [block] (init) {\Large Obtain sampling frame};
\node [block, below of = init] (contact) {\Large Contact eligible participants};
\node [block, below of = contact] (consent) {\Large Obtain consent};
\node [decision, below of = consent] (screening) {\Large Screening for cognitive function};
\node [block, right of = screening, node distance = 5cm] (refer) {\Large Refer to geriatric psychiatrists};
\node [block, below of = screening, node distance = 3.5cm] (assess0) {\Large Baseline assessment};
\node [block2, right of = contact, node distance = 5cm] (lifestyle) {\Large Administer lifestyle questionnaire};
\node [block2, right of = lifestyle, node distance = 4cm] (nutrition) {\Large Administer nutrition assessment};
\node [block2, right of = nutrition, node distance = 4cm] (blood) {\Large Take urine \& blood sample};
\node [block2, below of = nutrition, node distance = 3cm] (genetics) {\Large Genotyping};
\node [block2, below of = blood, node distance = 3cm] (metabolomics) {\Large Metabolomics profiling};
\node [block2, above of = nutrition] (assess) {\Large Assessment};
\node [decision, below of = assess0, node distance = 3cm] (followup) {\Large Follow-up screening pass?};
\node [decision, right of = followup, node distance = 5cm] (confirm){\Large Confirm by geriatric psychiatrists};
\node [block, right of = confirm, node distance = 4.8cm] (case){\Large Confirmed case};
\node [block, below of = followup, node distance = 3.5cm] (assessn) {\Large Repeated assessment};
\node [block, left of = followup, node distance = 4cm] (interval) {\Large Data processing};
\node [block, below of = assessn, node distance = 2.5cm] (end) {\Large End of study};
\node [block, below of = case, node distance = 3cm] (bloodcase) {\Large Take urine \& blood sample only};
% edges
\path [line] (init) -- (contact);
\path [line] (contact) -- (consent);
\path [line] (consent) -- (screening);
\path [line] (screening) -- node {eligible}(assess0);
\path [line] (screening) -- node {\Large no}(refer);
\path [line] (assess) -| (lifestyle);
\path [line] (assess) -- (nutrition);
\path [line] (assess) -| (blood);
\path [line] (blood) -- (metabolomics);
\path [line] (blood) |- ([xshift = -2.3cm, yshift = 1cm]metabolomics.north west) -- (genetics);
\path [line] (assess0) -- (followup);
\path [line] (followup) -- node {\Large no}(confirm);
\path [line] (followup) -- node {\Large yes}(assessn);
\path [line] (assessn) -| node {\Large 2 years}(interval);
\path [line] (interval) -- (followup);
\path [line] (confirm) -- node {\Large yes}(case);
\path [line] (confirm) |- node {\Large no}(assessn);
\path [line] (assessn) -- (end);
\path [line] (case) -- (bloodcase);
\end{tikzpicture}
\end{figure}
\end{document}