Remove "&" from bibliography in biblatex

Question

I have the following file:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[backend=biber, style=apa,natbib=true]{biblatex} 
\usepackage[english]{babel} 
\DeclareLanguageMapping{english}{english-apa}
\usepackage{hyperref}
\bibliography{\jobname.bib}
\ExecuteBibliographyOptions{doi=false,url=false, isbn=false}
\newbibmacro{string+doi}[1]{%
  \iffieldundef{doi}{#1}{\href{http://dx.doi.org/\thefield{doi}}{#1}}}
\DeclareFieldFormat{title}{\usebibmacro{string+doi}{\mkbibemph{#1}}}
\DeclareFieldFormat[article]{title}{\usebibmacro{string+doi}{#1}}
\DeclareFieldFormat{yearorunkyear}{%
  \ifthenelse{\iffieldequalstr{doubtfuldate}{true}}
    {\mkbibbrackets{ca\adddot\addspace#1}}
    {#1}}
\DeclareFieldFormat
  [article]
  {journaltitle}{{#1}}
\DeclareFieldFormat
  [article]
  {volume}{{(#1)}}

\begin{filecontents}{\jobname.bib}
@article{Yang2014,
annote = {The paper showed the importance of MIDAS or Mixed data sampling in studying the sentiment effect.},
author = {Yang, Chunpeng and Zhang, Rengui},
doi = {10.1080/00036846.2013.864041},
file = {:Users/Ahmed/Library/Application Support/Mendeley Desktop/Downloaded/Yang, Zhang - 2014 - Does mixed-frequency investor sentiment impact stock returns Based on the empirical study of MIDAS regression model.pdf:pdf},
issn = {0003-6846},
journal = {Applied Economics},
keywords = {M,investor sentiment,midas regression model,panel data model},
mendeley-tags = {M},
month = mar,
number = {9},
pages = {966--972},
title = {{Does mixed-frequency investor sentiment impact stock returns? Based on the empirical study of MIDAS regression model}},
url = {http://www.tandfonline.com/doi/abs/10.1080/00036846.2013.864041},
volume = {46},
year = {2014}
}
\end{filecontents}
\begin{document}
A reference to \cite{Yang2014}
\printbibliography
\end{document}

Which gives me:

I simply want to remove the & between authors names and put , instead.

Answer 1

Note that with this change you will lose APA-compliance. biblatex-apa implements the rules of the APA (quite) rigorously. If you have to follow APA, do not change anything (unless you think biblatex-apa does not respect the APA style, be sure to notify the author about that then); if you don't have to in many cases you are better off using a style that is easier to modify (in order to implement APA rules, biblatex-apa goes through quite some lengths and uses lots of code, which makes it sometimes harder to modify - not in this case, though).

Just go with

\AtBeginBibliography{\renewcommand*{\finalnamedelim}{\multinamedelim}}

We need \AtBeginBibliography here, because apa.bbx redefines the \finalnamedelim in an \AtBeginBibliography as well.

MWE

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[backend=biber, style=apa,natbib=true]{biblatex} 
\usepackage[english]{babel} 
\DeclareLanguageMapping{english}{english-apa}
\usepackage{hyperref}
\ExecuteBibliographyOptions{doi=false,url=false, isbn=false}
\newbibmacro{string+doi}[1]{%
  \iffieldundef{doi}{#1}{\href{http://dx.doi.org/\thefield{doi}}{#1}}}
\DeclareFieldFormat{title}{\usebibmacro{string+doi}{\mkbibemph{#1}}}
\DeclareFieldFormat[article]{title}{\usebibmacro{string+doi}{#1}}
\DeclareFieldFormat{yearorunkyear}{%
  \ifthenelse{\iffieldequalstr{doubtfuldate}{true}}
    {\mkbibbrackets{ca\adddot\addspace#1}}
    {#1}}
\DeclareFieldFormat
  [article]
  {journaltitle}{#1}
\DeclareFieldFormat
  [article]
  {volume}{\mkbibparens{#1}}

\begin{filecontents}{\jobname.bib}
@article{Yang2014,
annote = {The paper showed the importance of MIDAS or Mixed data sampling in studying the sentiment effect.},
author = {Yang, Chunpeng and Zhang, Rengui},
doi = {10.1080/00036846.2013.864041},
file = {:Users/Ahmed/Library/Application Support/Mendeley Desktop/Downloaded/Yang, Zhang - 2014 - Does mixed-frequency investor sentiment impact stock returns Based on the empirical study of MIDAS regression model.pdf:pdf},
issn = {0003-6846},
journal = {Applied Economics},
keywords = {M,investor sentiment,midas regression model,panel data model},
mendeley-tags = {M},
month = mar,
number = {9},
pages = {966--972},
title = {{Does mixed-frequency investor sentiment impact stock returns? Based on the empirical study of MIDAS regression model}},
url = {http://www.tandfonline.com/doi/abs/10.1080/00036846.2013.864041},
volume = {46},
year = {2014}
}
\end{filecontents}

\addbibresource{\jobname.bib}

\AtBeginBibliography{\renewcommand*{\finalnamedelim}{\multinamedelim}}


\begin{document}
A reference to \cite{Yang2014}
\printbibliography
\end{document}