Also, many exponents of filing knowledge have saidthat their file is a "fool-proof" one. I believe that youquestion this statement, as the only way to have afile as near perfect as possible, is to have safe andsane ideas and put them into practice; that is whythe Alphabetic file is the 95% file.
Alphabetic filing accounts for 95% of filing systems according to Butters.
The next Complex method in order, is the Numeric,which may be divided into three classes, straight num-eric, duplex and decimal. It is safe to say that withthe straight Alphabetic or Geographic, ninety-five per-cent of the cases where an Index is used will be moreefficiently handled by the use of either one of theseMethods, than by the Numeric. However, there aresome cases where there is a great deal of cross refer-ence, thus making the use of the Numeric methodmore advantageous.
This is likely the reason why most commonplacers using index card systems use alphabetic set ups by subject rather than Niklas Luhmann's duplex numeric variation.