The major points of extension from the original version of the paper


1. Only the qualitative discussion is given in the original paper, the quantitative discussion has been added.
    
In the original paper, two examples in which the analysis using the maximum likelihood method is inapplicable are shown. 
In the present paper, the condition under which the analysis is applicable is quantitatively discussed.
 
2. The quantification has altered the conclusion. 

Only from the qualitative discussion, we had to conclude that the analysis using the maximum likelihood method is not always applicable.
Based on the quantitative discussion, however, we can conclude that the method is applicable under an quantified condition.