I used the following Latex source file:
\RequirePackage{lineno}
\documentclass[aps,prl]{revtex4}
\usepackage{graphicx}% Include figure files
\usepackage{epstopdf} % this graphic package converts eps to pdf for easier usage of eps files
\usepackage{lpic}
\usepackage{amsmath,amssymb}
\usepackage{nicefrac}
\usepackage[utf8]{inputenc}
\usepackage{hyperref}
\usepackage{xcolor}
\usepackage{listingsutf8}
\usepackage[section]{placeins}
\lstset{mathescape=true}
\newcommand{\ket}[1]{\left|{#1}\right\rangle}
\newcommand{\bra}[1]{\left\langle{#1}\right|}
\newcommand{\is}[1]{{\color{blue} #1}}
\usepackage{subcaption}
\captionsetup{compatibility=false}
\begin{document}
\textbf{Corresponding author information}\\
Ad van der Ven, email: a.vanderven@pwo.ru.nl
\begin{figure}
\begin{subfigure}{0.50\textwidth}
{\bf Figure}
\caption{Based on the observed data sets}
\label{fig:RegressionFixedObservedN4451}
\end{subfigure}
\captionsetup{justification=raggedright,singlelinecheck=false}
\caption{Regression plot for the fixed condition of the ACT (N = 445). The
x-axis represents the natural logarithm of the absolute value of the minimum
residual score belonging to the sequence of 14 consecutive bars with the
smallest MSE. The y-axis represents the smallest MSE. The top line is the
line $y = 2x + \ln{10}$. The bottom line is the line $y = 2x-\ln{10}$. The
line exactly in between is the line $y=2x$.}
\label{fig:observedfixedcondion}
\end{figure}
\end{document}
However I do not want to have justification=raggedright nor justification=raggedleft. I simply want the caption aligned left and right. It seems justification does not have that option. I could not find an answer at 'Questions that may already have your answer'.


{}icon above the edit box. This will indent each line of code by 4 spaces in the edit box, which has the visual effect of rendering like code in the html page. – Steven B. Segletes Jan 08 '19 at 12:20\code=0`` – Steven B. Segletes Jan 08 '19 at 12:26captionandsubcaptionpackages are not compatible with revtex` package. see https://tex.stackexchange.com/questions/135718/caption-automatically-centered-in-a-revtex-document. – Zarko Jan 08 '19 at 12:46