documentclass[11pt,a4paper,toc=listof]{scrartcl}
usepackage[left=3cm, right=2cm, bottom=3cm, top=2cm]{geometry}
usepackage[english,ngerman]{babel} % Sprachpakete
usepackage[utf8]{inputenc}         % Direkte Eingabe von Umlauten
usepackage[T1]{fontenc}            % Worttrennung bei Umlauten
usepackage{microtype}              % Verbesserter Randausgleich
usepackage{textcomp}               % Zusätzliche Sonderzeichen
usepackage{graphicx}               % Einbindung Grafik
% Anführungszeichen
usepackage[
babel,
german=quotes,
german=guillemets
]{csquotes}
% ***** Bibliographie und Zitation *****
usepackage[
style           = apa,
sorting         = nyt,
sortcites       = true,
autocite        = inline,
maxbibnames     = 99,
maxcitenames    = 2,
backend         = biber,
bibliography    = totoc,
isbn            = false,
doi             = true,
urldate         = short
]{biblatex}
DeclareLanguageMapping{german}{german-apa}
DeclareFieldFormat{apacase}{#1}
DefineBibliographyStrings{ngerman}{%
andothers = {{et,aladddot}},
}
% remove comma in (Beadle and Tautum, 1941) This applies to citation only
renewcommand*{nameyeardelim}{addspace}
% change delimiters
renewcommand*{multinamedelim}[0]{,/,}
renewcommand*{finalnamedelim}[0]{,/,}
AtBeginBibliography{%
    renewcommand*{multinamedelim}[0]{,/,}%
    renewcommand*{finalnamedelim}[0]{,/,}%
}
% Umbrüche in URL und DOI bei Zahlen zulassen
setcounter{biburlnumpenalty}{100}  % allow breaks at numbers
% Reihen in Bibliographie
DeclareFieldFormat{number}{bibstring{number}~#1}
% name sort always last, first
AtBeginBibliography{%
DeclareNameAlias{editor}{last-first}
}
% Anpassungen um Schriftenreihe mit Nummer vor Ort und Verlag zu platzieren
renewbibmacro*{addinfo}{%
    ifthenelse{iffieldundef{edition}AND%
          iffieldundef{chapter}AND%
          iffieldundef{volumes}AND%
          iffieldundef{pages}AND%
          (iffieldundef{volume}ORboolean{bbx:volseen})}
    {}
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    printfield{chapter}%
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    setunit{}%
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renewbibmacro*{maintitle+title}{%
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      printfield{volume}%
      printfield{part}%
      setunit{adddotspace}}}}%
    usebibmacro{title}%
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renewbibmacro*{maintitle+booktitle}{%
 ifthenelse{iffieldundef{maintitle}ANDiffieldundef{booktitle}}
{}
{usebibmacro{in}%
 iffieldundef{maintitle}
  {}
  {usebibmacro{maintitle}%
   newunitnewblock
   iffieldundef{volume}
     {}
     {setunit{addspaceglobalbooltrue{bbx:volseen}}%
      printfield{volume}%
      printfield{part}%
      setunit{adddotaddspace}}}%
usebibmacro{booktitle}}}
renewbibmacro*{series+number}{%
    printfield{series}%
    setunit{addcommaspace}%
    printfield{number}%
    newunit}
usepackage{xpatch}
    xpatchbibdriver{book}
    {printfield{series}}
    {usebibmacro{series+number}}
    {}{}
    xpatchbibdriver{inbook}
    {printfield{series}}
    {usebibmacro{series+number}}
    {}{}
    xpatchbibdriver{incollection}
    {printfield{series}}
    {usebibmacro{series+number}}
    {}{}
    xpatchbibdriver{collection}
    {printfield{number}}
    {}
    {}{}
    xpatchbibdriver{collection}
    {printfield{series}}
    {usebibmacro{series+number}}
    {}{}
% Eintragsart Bericht (report) Anpassung
DeclareFieldFormat[report]{number}{bibcpstring{number}~apanum{#1}}
    renewbibmacro*{apa:reportnum}{%
    newunitnewblock
    printfield{type}%
    setunit*{addcommaspace}%
    printfield{number}}
xpatchbibdriver{report}
      {printlist{institution}}
    {}
    {}{}
newbibmacro*{location+institution}{%
    printlist[default][1-1]{location}%
    setunit*{addcolonspace}%
    printlist{institution}%
    newunit}
xpatchbibdriver{report}
    {usebibmacro{location+publisher}}
    {usebibmacro{location+institution}}
    {}{}
% bei allen Eintragsarten andere Editortypen missachten
AtEveryBibitem{
    iffieldequalstr{editortype}{redactor}
    {globalclearname{editor}typeout{delete editor (type: redactor) in thefield{citekey}}}{}%
    iffieldequalstr{editoratype}{redactor}
    {globalclearname{editora}typeout{delete editora (type: redactor) in thefield{citekey}}}{}%
    iffieldequalstr{editorbtype}{redactor}
    {globalclearname{editorb}typeout{delete editorb (type: redactor) in thefield{citekey}}}{}%
    iffieldequalstr{editorctype}{redactor}
    {globalclearname{editorc}typeout{delete editorc (type: redactor) in thefield{citekey}}}{}%
    }
% Alle Zitate in Kurzform (ab 3 Autoren et al.), bereits ab erster Nennung
usepackage{filecontents}
begin{filecontents}{jobname.bib}
@book{Backhaus.etal_2015,
langid = {Deutsch},
location = {{Berlin}},
title = {Fortgeschrittene Multivariate Analysemethoden textemdash{} Eine anwendungsorientierte Einf{"u}hrung},
edition = {3., {"u}berarb. u. akt. Aufl.},
isbn = {978-3-662-46086-3},
publisher = {{Springer Gabler}},
date = {2015},
author = {Backhaus, Klaus and Erichson, Bernd and Weiber, Rolf}
}
@book{Backhaus.etal_2016,
langid = {Deutsch},
location = {{Berlin}},
title = {Multivariate Analysemethoden textemdash{} Eine anwendungsorientierte Einf{"u}hrung},
edition = {14., {"u}berarb. u. akt. Aufl.},
isbn = {978-3-662-46075-7},
publisher = {{Springer Gabler}},
date = {2016},
author = {Backhaus, Klaus and Erichson, Bernd and Plinke, Wulff and Weiber, Rolf}
}
@report{Revelle_2017b,
langid = {Englisch},
location = {{Evanston$backslash$IL}},
title = {How To: Use the psych package for Factor Analysis and data reduction},
url = {http://personality-project.org/r/psych/HowTo/factor.pdf},
institution = {{Department of Psychology, Northwestern University}},
urldate = {2018-07-01},
date = {2017},
author = {Revelle, William}
}
@incollection{Revelle.Condon_2018,
langid = {Englisch},
location = {{Chichester}},
title = {Reliability},
volume = {2},
isbn = {978-1-118-48977-2},
volumes = {2},
booktitle = {The Wiley Handbook of Psychometric Testing textemdash{} A Multidisciplinary Reference on Survey, Scale and Test Development},
publisher = {{J. Wiley & Sons}},
date = {2018},
pages = {709-749},
author = {Revelle, William and Condon, David M.},
editor = {Irwing, Paul and Booth, Tom and Hughes, David J.},
doi = {10.1002/9781118489772.ch23}
}
@article{Revelle.Zinbarg_2009,
langid = {Englisch},
title = {Coefficients Alpha, Beta, Omega, and the GLB textemdash{} Comments on Sijtsma},
volume = {74},
issn = {0033-3123, 1860-0980},
doi = {10.1007/s11336-008-9102-z},
shorttitle = {Coefficients Alpha, Beta, Omega, and the glb},
number = {1},
journaltitle = {Psychometrika},
date = {2009},
pages = {145-154},
author = {Revelle, William and Zinbarg, Richard E.}
}
@article{Wright.Herrington_2011,
langid = {Englisch},
title = {Problematic Standard Errors and Confidence Intervals for Skewness and Kurtosis},
volume = {43},
issn = {1554-3528},
doi = {10.3758/s13428-010-0044-x},
number = {1},
journaltitle = {Behavior Research Methods},
date = {2011},
pages = {8-17},
author = {Wright, Daniel B. and Herrington, Joshua A.}
}
end{filecontents}
addbibresource{jobname.bib}
% ******************* T E X T *******************%
begin{document}
Source 1: cite[8]{Wright.Herrington_2011}
Source 2: cite[154]{Revelle.Zinbarg_2009}
Source 3: cite{Revelle_2017b}
Source 4: cite{Backhaus.etal_2016}
Source 5: cite{Backhaus.etal_2015}
Source 6: cite{Backhaus.etal_2016}
Source 7: cite{Backhaus.etal_2015}
Source 8: cite{Revelle.Condon_2018}
newpage
printbibliography[title=Literaturverzeichnis]
end{document}