Final answer:
The method described for measuring sentiment by the proportion of negative to total words is best understood as part of sentiment analysis in NLP, although none of the provided options (A, B, C, D) accurately name this method.
Step-by-step explanation:
The method that measures the proportion of negative words to total words to measure sentiment is not explicitly provided in the options, but such a method is typically known as sentiment analysis or sentiment scoring in the field of Natural Language Processing (NLP).
However, none of the provided options (A) Negative proportion, B) Sentiment index, C) Negative ratio, D) Overlap) accurately describe this method. In sentiment analysis, the calculation of the proportion of negative to total words would be part of a larger algorithm used to determine the overall sentiment index or score, which could be positive, neutral, or negative. It's important to note that the given options from A to D relate to different concepts that do not directly describe sentiment analysis tools or techniques.