I do not know where the problem is but I have issues centering tables. I have tried \centering and \begin{center} but they are still left-aligned. Does someone of you know where the problem lies?
\documentclass[paper=a4, pagesize, fontsize=11pt]{scrartcl}
\usepackage[utf8]{inputenc} % Eingabekodierung
\usepackage[T1]{fontenc} % Fontkodierung
\usepackage[ngerman]{babel} % deutsche Sprachenunterstützung; Doku: "gerdoc"
\usepackage{tabularx, siunitx,booktabs, float}
\setkomafont{captionlabel}{\small\sffamily\bfseries} % kleinere Beschriftungen
\addtokomafont{caption}{\small}
\renewcommand{\arraystretch}{1}
\begin{document}
\begin{table}[H]
\centering
\caption{Ergebnisse des Martin-Loef-Tests}
\label{tab:mltest}
\footnotesize
\begin{tabular*}{0.7\textwidth}{
@{\extracolsep{\fill}}% fill the space between columns
l % one left aligned column
*{3}{c} }
\toprule
{Dimension}&{\emph{LR}} & {\emph{df}} & {$p$}\\ \midrule
UEBE & {331.48} & {255} & {.001}\\
SOUE & {161.92} & {143} & {\phantom{0}.13}\\
ERDR & {211.74} & {319} & {\phantom{0}.99}\\
UNZU & {167.18} & {255} & {\phantom{0}.99}\\
UEFO & {\phantom{1}95.37} & {143} & {\phantom{0}.99}\\
MANG &{\phantom{1}99.40}& {63}& {.002} \\
SOZS &{103.71}&{143}& {\phantom{0}.99}\\
SOZI &{115.44} &{143}& {\phantom{0}.96}\\
SORG &{\phantom{1}68.28}& {63}& {\phantom{0}.30} \\
\bottomrule
\end{tabular*}
\scriptsize{
\begin{tablenotes}
\item UEBE: Arbeitsüberlastung; SOUE: Soziale Überlastung; ERDR: Erfolgsdruck; UNZU: Arbeitsunzufriedenheit;
\item UEFO: Überforderung; MANG: Mangel an sozialer Anerkennung; SOZS: Soziale Spannungen; SOZI: Soziale Isolation; SORG: Chronische Besorgnis
\end{tablenotes}}
\end{table}
\begin{table}[H]
\centering
\begin{threeparttable}
\caption{Schätzung der Itemparameter für UEBE -- MANG}
\label{tab:itempar}
\setlength{\tabcolsep}{0pt}
\footnotesize
\begin{tabular*}{0.75\textwidth}{
@{\extracolsep{\fill}}% fill the space between columns
l % one left aligned column
*{2}{S[table-format=1.2]S[table-format=-1.2]}S[table-format=0.3,table-space-text-pre=$<{}$]}
\toprule
Items & {Lokalisation} &{$\tau_{i1}$}& {$\tau_{i2}$} &{$\tau_{i3}$}& {$\tau_{i4}$}\\
\midrule
\textbf{\emph{UEBE}} &&&&&\\ \midrule
TICS 1 &1.08 &-0.82 & 0.04 & 1.89 & 3.20\\
TICS 4 &0.96 &-1.81 & 0.14 & 2.13 & 3.37\\
TICS 17 &0.79 &-1.76 & 0.02 & 1.97 & 2.92\\
TICS 27 &0.91 &-1.09 & 0.78 & 1.19 & 2.75\\
TICS 38 &0.80 &-1.94 &-0.11 & 1.87 & 3.40 \\
TICS 44 &0.55 &-1.58 &-0.48 & 1.28 & 2.96\\
TICS 50 &0.72 &-1.95 &-0.03 & 1.53 & 3.35\\
TICS 54 &0.47 &-1.75 &-0.51 & 1.44 & 2.72\\
\addlinespace
\textbf{\emph{SOUE}}&&&&&\\ \midrule
TICS 7 & 0.17 &-1.23 &-0.03 &0.74 & 1.18\\
TICS 19 & 0.83 &-0.76 &0.83 &0.95 & 2.29 \\
TICS 28 &0.64 &-1.14 &0.45 &1.38 & 1.85\\
TICS 39 &-0.05 &-2.03 &-0.55 &0.87 & 1.49\\
TICS 49 &0.43 &-1.23 &0.18 &1.42 & 1.35 \\
TICS 57 &0.98 &-0.92 &0.54 &1.77 & 2.52\\
\addlinespace
\textbf{\emph{ERDR}}&&&&&\\ \midrule
TICS 8 & 0.54 &-1.67 &-0.05 &1.63 &2.25\\
TICS 12 & 0.81 &-1.73 & 0.35 &2.09 &2.54\\
TICS 14 & 0.75 &-1.21 & 0.25 &1.82 &2.16\\
TICS 22 & 0.38 &-1.86 & 0.54 &0.61 &2.24\\
TICS 23 & 0.22 &-1.44 & -0.30&0.57 &2.04\\
TICS 30 & 0.61 &-1.94 & -0.07&1.58 &2.86\\
TICS 32 &1.27 &-0.76 & 0.76 &2.07 &2.99\\
TICS 40 &0.98 &-1.05 & 0.54 &1.54 &2.88\\
TICS 43 &0.41 &-2.15 & 0.08 &1.46 &2.26\\
\addlinespace
\textbf{\emph{UNZU}}&&&&&\\ \midrule
TICS 5 &0.21 &-1.25 &-0.53 &1.00 &1.61\\
TICS 10 &0.30 &-1.41 &-0.69 &1.44 &1.85\\
TICS 13 &-0.13&-3.04 &-0.54 &1.41 &1.63\\
TICS 21 &0.84 &-0.84 &0.44 &1.89 &1.89\\
TICS 37 & 1.49&0.24 &1.32 &2.14 &2.26 \\
TICS 41 &0.79 &-1.24 &0.61 &2.16 &1.64\\
TICS 48 &0.34 &-1.59 &-0.23 &0.88 &2.30\\
TICS 53 &0.45 &-1.27 &0.27 &1.80 &0.99\\
\addlinespace
\textbf{\emph{UEFO}}&&&&&\\ \midrule
TICS 3 & 0.91 & -2.24 & 0.73 & 2.69 & 2.45\\
TICS 20 & 1.31 &-1.41 & 1.42 & 2.47 & 2.74 \\
TICS 24 &0.87 &-1.32 & 0.38 & 2.31 & 2.10\\
TICS 35 & 0.58 &-2.63 & 0.20 & 2.64 & 2.11\\
TICS 47 & 0.09 &-2.49 &-0.17 & 0.85 & 2.20\\
TICS 55 & 0.63 &-2.12 &0.57 & 1.86 & 2.21\\
\addlinespace
\textbf{\emph{MANG}}&&&&&\\ \midrule
TICS 2 &0.34 & -3.16 &-0.48 & 1.72 & 3.29\\
TICS 18 &1.37 &-1.64 &0.82 & 2.56 & 3.75\\
TICS 31 &1.13 &-1.85 &0.53 & 2.59 & 3.27\\
TICS 46 &0.84 &-2.00 &0.10 & 2.35 & 2.91\\
\bottomrule
\end{tabular*}
\end{threeparttable}
\scriptsize{
\begin{tablenotes}
\item UEBE: Arbeitsüberlastung; SOUE: Soziale Überlastung; ERDR: Erfolgsdruck; UNZU: Arbeitsunzufriedenheit; UEFO: Überforderung; MANG: Mangel an sozialer Anerkennung; SOZS: Soziale Spannungen; SOZI: Soziale Isolation; SORG: Chronische Besorgnis
\end{tablenotes}}
\end{table}
\end{document}
Thank you very much for your help.
\scriptsizedoes not take arguments. Additionally I would probably not usetabular*heresiunitxin the second table, but not in the first one? You could remove all the\phantomcommands if you usedsiunitx. Please also clarify: Do you want caption and table notes to be as wide as the table or as wide as the whole textwidth. Why did you stretch the table to be that wide? Couldn't you place the long versions of the abbreviations in the table itself instead of below it? What's the reason to use\footnotesizefor the first table? It would fit perfectly if you used a normalsize font.