Is “sentiment analysis” doing anything real?

Oceans of computational cycles have been spent analysing the sentiment of documents, driven by businesses interested in how their products are being perceived, movie producers interested in their potential products, and just about everyone about tweets.

Sentiment is based on a measure of how “positive” or “negative” a particular document is. The problem is that there are a number of aspects of an individual that could be positive or negative, and sentiment analysis jams them all into one bucket and measures them. It’s far from clear that this measures anything real — signs of which can be seen in the well-known one-and-a-half star difference when individuals are asked to rate the same objects on two successive days.

So what can be positive and negative?

It could be the individual’s attitude to a particular object and, of course, this is what most systems purport to be measuring. However, attitude is a two-place relation: A’s attitude to B. It’s usually obvious that a document has been written by A, but much more difficult to make sure that the object about which the attitude is being expressed is actually B.

However, most of the difficulty comes from other aspects that can also be positive and negative. One of these is mood. Mood is an internal setting whose drivers are poorly understood but which is known to be (a) predictable over the course of a period of, say, a day, and (b) composed of two independent components, positive mood and negative mood (that is, not opposites). In broad brush terms, negative mood is stable through the day, while positive mood peaks in the middle of the day. There are longer term patterns as well; positive mood tends to increase through the week while negative mood decreases.

Looking at someone’s writing about an object therefore should take into account their underlying mood — but never does. And it would be difficult to tease apart the signals of mood from the signals of attitude with the current state of the art. But we could plausibly predict that “sentiment” would be less positive overall if it was captured at the beginning or end of the day.

The other aspect that can be positive or negative is emotion. Emotions are short-term responses to the current environment that play a role in reordering each individual’s priorities to optimize decision making, especially in response to an external stimulus.  There are two emotions that align strongly with positivity (joy) and negativity (disgust).

Looking at someone’s writing about an object should therefore take into account their emotional state (at the time they were writing) — but never does. Again it would be difficult to tease the signals of emotion and the signals of attitude apart. I have no doubt that many businesses get much worse results from their surveys than they ‘should’ because those surveys are designed so poorly that they become annoying, and this spills over into the content of the responses.

Bottom line: there is no such thing as positive sentiment or negative sentiment. There are positive or negative attitudes, moods, and emotions, but the one that sentiment analysis is trying to measure — attitudes — is inextricably confounded by the other two.  Progress is being made in understanding and detecting moods and emotions, but much less has been done on detecting attitudes, mostly because of the difficulty of finding the intended object within a short piece of text.

 

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