Help to obtain a professional table (using Latex)

Question

Could you please show me how to improve the table below? In particular:

1) is it correct to put the "(%)", in the caption? Otherwise how could I point out that the numbers of the table are percentages?

2) is it correct to put the additional column header before the row "Corporate"?

3) How to better distribute colums?

The LaTeX code to obtain the table is this:

\documentclass[11pt,openright]{book}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage[a4paper]{geometry}
\geometry{verbose,tmargin=3cm,bmargin=3.5cm,lmargin=4cm,rmargin=3cm}
\pagenumbering{gobble}
\usepackage{booktabs}
\usepackage{tabulary}
\usepackage[flushleft]{threeparttable}
\usepackage[font=small,labelfont=bf,labelsep=period,format=hang,indention=0cm]{caption}
\captionsetup[table]{position=above, belowskip=10pt}

\begin{document}

\begin{threeparttable}[b]
    \caption{Weights (\%) depending upon ratings in the Standardise Approach of Basel II}
    \footnotesize{}
    \begin{tabulary}{\textwidth}{@{}LRRRRRR@{}}
        \toprule 
        & \multicolumn{6}{c}{{\footnotesize{}Rating\tnote{a}}}\tabularnewline   
        \cmidrule{2-7}
        {Category of claims} & {AAA to AA-} & {A+ to A-} & {BBB+ to BBB-} & {BB+ to B-} & {Below B-} & {Unrated}\tabularnewline
        \midrule
        {Sovereigns} & {0} & {20} & {50} & {100} & {150} & {100}\tabularnewline
        {Non-central government PSEs (option 1)} & {20} & {50} & {100} & {100} & {150} & {100}\tabularnewline
        {Non-central government PSEs (option 2)} & {20} & {50} & {50} & {100} & {150} & {50}\tabularnewline
        {MDBs} & {20} & {50} & {50} & {100} & {150} & {50}\tabularnewline
        {Banks (option 1)} & {20} & {50} & {100} & {100} & {150} & {100}\tabularnewline
        {Banks (option 2)} & {20} & {50} & {50} & {100} & {150} & {50}\tabularnewline
        {Banks (option 2 - short-term claims)} & {20} & {20} & {20} & {50} & {150} & {20}\tabularnewline
        &  &  & \multicolumn{2}{r}{{BBB+ to BB-}} & {Below BB-} & \tabularnewline
        \cmidrule{4-6} 
        {Corporate} & {20} & {50} & \multicolumn{2}{r}{{100}} & {150} & {100}\tabularnewline
        \bottomrule
    \end{tabulary}
    \begin{tablenotes}
        \item [a] \footnotesize{}The rating notations are by Standard \& Poor's but only for example,
        those of some other credit assessment institutions could be used. \\
        \footnotesize{}\emph{Source}: based on BCBS (2006).
    \end{tablenotes}
\end{threeparttable}

\end{document}

Answer 1

You asked:

1. is it correct to put the "(%)", in the caption? Otherwise how could I point out that the numbers of the table are percentages?
2. is it correct to put the additional column header before the row "Corporate"?
3. How to better distribute colums?

Well, at last it depends on the used language for the document (you seems to be a German) and the rules for the used typography in this language. Please have a look to this question for relevant books or papers.

Answers to your questions:

1. I'm used to write tables with the relevant units in the column header, so in your case that should be your column header [%]. I have a little problem to understand your table: your main column heading is Ratings and then you show for example unrated [%]. But the given numbers 150 or 100 seems to mean 150% or 100%. And there is no possibility to have sums of columns or rows resulting in 100%. So I'm not sure where to place the unit unmissunderstandable ...
2. The additional column header marks a new table in my opinion. So I would write for example two tables 1a and 1b to show that there is an break in the headings. Remember: A thesis should be unmissunderstandable and so it is better to reference situation 1 in table 1a and situation 2 in table 1b. And do not forget to reference each table for minimum one time!
3. A table should be as symetric as it can be. So if you have numbers inside make the columns as wide as needed and as narrow as possibe. That could result in setting the header of the columns turned for 90 degree or less. If possible use short, but understandable headings and omit line breaks inside. If you need to have linebreaks break the line where it makes sense : Donaudampfschiffahrts-gesellschafts-kapitänsmütze (German example). Then keep the numbers centered vertically in the cell.

Do not use lines if possible, use better two different colors to mark columns or rows.

If your headings are too long you can define abreviations (and add them to your glossary!) before you reference the table the first time. Try to have the table in the same font size your document is. If needed use not too small font size for the table ...

At last can you explain your table a little bit? I'm really not sure how to write your unit % in it ...

Answer 2

First of all, check if there are any preferred style guides you should be following. If there are, there should be guidelines for the use of tables and units etc.

With regards to the units—I don't see any problem with stating the unit in the caption, but I would personally declare it in the column header. If the columns used different units, you would declare the unit in the header for that column. Since the whole table uses the same units you can declare it in the "Rating" header. The closer to the value you declare the units the better.

I personally don't like tables without anything differentiating the columns or rows—it isn't good for usability. I would add borders to the columns and rows, making use of thinner or lighter borders.

Another thing to keep in mind is the row heights. Varying row heights when the actual values are all the same height can be confusing. Try and keep the row labels on one line, use abbreviations or shorter terms if possible.

The breaks in the column header should be consistent too. If you can't avoid the line-breaks, manually break in a consistent way. I would break before the "to" in each header.

Something like this:

An alternatives to borders is using alternating backgrounds:

Compare the first example with the original row labels:

This, in my opinion, isn't as readable and looks untidy. If you can't shorten the row labels and keep them on one line, another option is to increase all the row heights to fit the largest label, keeping a consistent height and vertically centering the cell content. The following example looks a lot better but takes up a lot more page space:

With regards to the additional columns—Adding the additional column headers before the "Corporate" row is a perfectly acceptable solution. Wether it is the best option depends on the situation. If you have a lot of horizontal space to work with it may be better to have all the columns span the whole table:

How to do any of this in LaTeX I have no idea... You would be better asking that on LaTeX Stack Exchange. It's also worth noting that I have no idea what any of this data means so there may be some data-specific details I'm missing or getting wrong.