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A beginner’s guide to natural language sentiment analysis

An image of five faces ranging from angry to happy.
22 July 2018

Sentiment analysis (sometimes called “opinion mining” or “emotion AI”) is a Natural Language Processing (NLP) technique to categorize text depending on whether it expresses an opinion and whether the opinion is positive, negative, or neutral. Advanced sentiment analysis can also categorize text by emotional state like angry, happy, or sad. It is often used in customer experience, user research, and qualitative data analysis on everything from user feedback and reviews to social media posts.

Sentiment analysis can be combined with Machine Learning (ML) to further categorize text by topic. Together, sentiment analysis and machine learning provide researchers with a method to automate the analysis of lots of qualitative textual data in order to identify patterns and track trends over time.

Sentiment analysis by example

The easiest way to quickly understand what sentiment analysis can do for you is by looking at examples. Take the following three sentences:

  1. I love flying Air New Zealand because they have the best food.

  2. That orange Fiat Multipla is the ugliest car I’ve ever seen.

  3. I love this phone but wouldn’t recommend it to my friends.

As a human, you can read the first sentence and determine the person is offering a positive opinion about Air New Zealand. The second sentence is offering a negative opinion, and the last is also a negative opinion, although it’s a little harder to parse.

You had to read each sentence manually and determine the sentiment, whereas sentiment analysis, on the other hand, can scan and categorize these sentences for you as positive, negative, or neutral.

Like humans, sentiment analysis looks at sentence structure, adjectives, adverbs, magnitude, keywords, and more to determine the opinion expressed in the text. The advantage of sentiment analysis is that it’s much, much quicker.

Use cases for sentiment analysis

Sentiment analysis has many practical use cases in customer experience, user research, qualitative data analysis, social sciences, and political research.

Analyzing user feedback

Sentiment analysis is great for quickly analyzing user’s opinion on products and services, and keeping track of changes in opinion over time. For example, users of Dovetail can connect to apps like Intercom and UserVoice; when user feedback arrives from these sources, Dovetail’s sentiment analysis automatically tags it.

Categorizing reviews

Reviews are a perfect candidate for sentiment analysis since they’re written in the first person, and by their very nature, are offering an opinion. Reviews could be for hotels, airlines, rental cars, Amazon purchases, mobile apps, or anything else. Dovetail is great for analyzing reviews; users simply upload a spreadsheet of reviews and Dovetail automatically tags sentences with ‘Positive’ and ‘Negative’.

Analyzing social media posts

Sentiment analysis is often used by researchers in combination with Twitter, Facebook, or YouTube’s API. A popular use case is trying to predict elections based on the sentiment of tweets leading up to election day.

Pros and cons of sentiment analysis

Sentiment analysis works best with large data sets written in the first person, where the nature of the data invites the author to offer a clear opinion.


  • Great for quickly analyzing thousands—or even millions—of pieces of data where topic categorization is less important than an overall indication of sentiment.

  • Can give you a starting point in qualitative data analysis by extracting strongly positive or negative sentences out of documents.

  • Works particularly well with data where the author clearly expresses an opinion (e.g. app reviews, political views, user feedback).

  • Somewhat context-agnostic – it doesn’t matter if the data is about politics, mobile phone reviews, cooking recipes, or anything.

  • Some providers (e.g. Google and Amazon) have support for multiple languages.


  • Not a replacement for ML auto-categorization as it will only categorize text based on its sentiment, not the topic discussed.

  • Does not work well on text written in the third person(e.g. user testing observations) or where the data is not someone’s opinion on a product or service.

  • Can struggle with complex sentences involving double negatives, sarcasm, adverbials, unknown proper nouns and brand names, and greetings (e.g. “Best wishes!” or “Looking forward to your response” in email signatures).

How sentiment analysis works

Interested in how it actually works? There are three main approaches to sentiment analysis. These are knowledge-basedstatistical methods, and hybrid approaches.

Knowledge-based sentiment analysis

Knowledge-based techniques categorize text based on unambiguous ‘affect words’ like love, like, hate, happy, sad, angry, and so on. This is the simplest and oldest sentiment analysis technique, and also probably the least accurate. It works best on simple sentences like “I love cake” or “I dislike mushrooms.”

Statistical sentiment analysis

Statistical methods use elements from machine learning where affect words are derived from a model trained on millions of other examples, along with advanced Natural Language Processing (NLP), where the computer detects the holder of a sentiment (the person with the opinion) and the target (the product or service) in a sentence. This approach can handle more complex sentences like “I don’t not like cheeseburgers”.

Hybrid sentiment analysis

A hybrid approach uses a combination of the above techniques, with the addition of an advanced understanding of language in order to detect semantics that are expressed in a subtle manner, e.g. building relationships between implicit and explicit concepts.

Other NLP techniques

Sentiment analysis is one of many NLP techniques. Other techniques that are helpful for user research and qualitative data analysis include:

Start using sentiment analysis today

You can start using sentiment analysis in a variety of ways:

  • Open source tools. While free and flexible, these often require significant setup and may only run on certain operating systems.

  • Online APIs. Amazon ComprehendGoogle Cloud, and Microsoft Azure offer paid Natural Language APIs which are designed for large scale operation but require programming experience to configure.

  • SaaS products. Companies like Dovetail include sentiment analysis in easy-to-use features that require no data science or programming experience.

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