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A paper recently published in PNAS claims that human language tends to be positive. This was news enough to make the New York Times. But there are a few fundamental problems with the paper.

Linguistics – Now with less linguists!

The first thing you might notice about the paper is that it was written by mathematicians and computer scientists. I can understand the temptation to research and report on language. We all use it and we feel like masters of it. But that’s what makes language a tricky thing. You never hear people complain about math when they only have a high-school-level education in the subject. The “authorities” on language, however, are legion. My body has, like, a bunch of cells in it, but you don’t see me writing papers on biology. So it’s not surprising that the authors of this paper make some pretty basic errors in doing linguistic research. They should have been caught by the reviewers, but they weren’t. And the editor is a professor of demography and statistics, so that doesn’t help.

Too many claims and not enough data

The article is titled “Human language reveals a universal positivity bias” but what the authors really mean is “10 varieties of languages might reveal something about the human condition if we had more data”. That’s because the authors studied data in 10 different languages and they are making claims about ALL human languages. You can’t do that. There are some 6,000 languages in the world. If you’re going to make a claim about how every language works, you’re going to have to do a lot more than look at only 10 of them. Linguists know this, mathematicians apparently do not.

On top of that, the authors don’t even look at that much linguistic data. They extracted 5,000–10,000 of the most common words from larger corpora. Their combined corpora contain the 100,000 most common words in each of their sub-corpora. That is woefully inadequate. The Brown corpus contains 1 million words and it was made in the 1960s. In this paper, the authors claim that 20,000 words are representative of English. That is, not 20,000 different words, but the 5,000 most common words in each of their English sub-corpora. So 5,000 words each from Twitter, the New York Times, music lyrics, and the Google Books Project are supposed to represent the entire English language. This is shocking… to a linguist. Not so much to mathematicians, who don’t do linguistic research. It’s pretty frustrating, but this paper is a whole lotta ¯\_(ツ)_/¯.

To complete the trifecta of missing linguistic data, take a look at the sources for the English corpora:

Corpus Word count
English: Twitter 5,000
English: Google Books Project 5,000
English: The New York Times 5,000
English: Music lyrics 5,000

If you want to make a general claim about a language, you need to have data that is representative of that language. 5,000 words from Twitter, the New York Times, some books and music lyrics does not cut it. There are hundreds of other ways that language is used, such as recipes, academic writing, blogging, magazines, advertising, student essays, and stereo instructions. Linguists use the terms register and genre to refer to these and they know that you need more than four if you want your data to be representative of the language as a whole. I’m not even going to ask why the authors didn’t make use of publicly available corpora (such as COCA for English). Maybe they didn’t know about them. ¯\_(ツ)_/¯

Say what?

Speaking of registers, the overwhelmingly most common way that language is used is speech. Humans talking to other humans. No matter how many written texts you have, your analysis of ALL HUMAN LANGUAGE is not going to be complete until you address spoken language. But studying speech is difficult, especially if you’re not a linguist, so… ¯\_(ツ)_/¯

The fact of the matter is that you simply cannot make a sweeping claim about human language without studying human speech. It’s like doing math without the numeral 0. It doesn’t work. There are various ways to go about analyzing human speech, and there are ways of including spoken data into your materials in order to make claims about a language. But to not perform any kind of analysis of spoken data in an article about Language is incredibly disingenuous.

Same same but different

The authors claim their data set includes “global coverage of linguistically and culturally diverse languages” but that isn’t really true. Of the 10 languages that they analyze, 6 are Indo-European (English, Portuguese, Russian, German, Spanish, and French). Besides, what does “diverse” mean? We’re not told. And how are the cultures diverse? Because they speak different languages and/or because they live in different parts of the world? ¯\_(ツ)_/¯

The authors also had native speakers judge how positive, negative or neutral each word in their data set was. A word like “happy” would presumably be given the most positive rating, while a word like “frown” would be on the negative end of the scale, and a word like “the” would be rated neutral (neither positive nor negative). The people ranking the words, however, were “restricted to certain regions or countries”. So, not only are 14,000 words supposed to represent the entire Portuguese language, but residents of Brazil are rating them and therefore supposed to be representative of all Portuguese speakers. Or, perhaps that should be residents of Brazil with internet access.

[Update 2, March 2: In the following paragraph, I made some mistakes. I should not have said that ALL linguists believe that rating language is an notoriously poor way of doing an analysis. Obviously I can’t speak for all the linguists everywhere. That would be overgeneralizing, which is kind of what I’m criticizing the original paper for. Oops! :O I also shouldn’t have tied the rating used in the paper and tied it to grammaticality judgments. Grammaticality judgments have been shown to be very, very consistent for English sentences. I am not aware of whether people tend to be as consistent when rating words for how positive, negative, or neutral they are (but if you are, feel free to post in the comments). So I think the criticism still stands. Some say that the 384 English-speaking participants is more than enough to rate a word’s positivity. If people rate words as consistently as they do sentences, then this is true. I’m not as convinced that people do that (until I see some research on it), but I’ll revoke my claim anyway. Either way, the point still stands – the positivity of language does not lie in the relative positive or negative nature of the words in a text (the next point I make below). Thanks to u/rusoved, u/EvM and u/noahpoah on reddit for pointing this out to me.] There are a couple of problems with this, but the main one is that having people rate language is a notoriously poor way of analyzing language (notorious to linguists, that is). If you ask ten people to rate the grammaticality of a sentence on a scale from 1 to 10, you will get ten different answers. I understand that the authors are taking averages of the answers their participants gave, but they only had 384 participants rating the English words. I wouldn’t call that representative of the language. The number of participants for the other languages goes down from there.

A loss for words

A further complication with this article is in how it rates the relative positive nature of words rather than sentences. Obviously words have meaning, but they are not really how humans communicate. Consider the sentence Happiness is a warm gun. Two of the words in that sentence are positive (happiness and warm), while only one is negative (gun). This does not mean it’s a positive sentence. That depends on your view of guns (and possibly Beatles songs). So it is potentially problematic to look at how positive or negative the words in a text are and then say that the text as a whole (or the corpus) presents a positive view of things.

Lost in Google’s Translation

The last problem I’ll mention concerns the authors’ use of Google Translate. They write

We now examine how individual words themselves vary in their average happiness score between languages. Owing to the scale of out corpora, we were compelled to use an online service, choosing Google Translate. For each of the 45 language pairs, we translated isolated words from one language to the other and then back. We then found all word pairs that (i) were translationally stable, meaning the forward and back translation returns the original word, and (ii) appeared in our corpora in each language.

This is ridiculous. As good as Google Translate may be in helping you understand a menu in another country, it is not a good translator. Asya Pereltsvaig writes that “Google Translate/Conversation do not translate. They match. More specifically, they match (bits of) the original text with best translations, where ‘best’ means most frequently found in a large corpus such as the World Wide Web.” And she has caught Google Translate using English as an intermediate language when translating from one language to another. That means that when going between two languages that are not English (say French and Russian), Google Translate will first translate the word into English and then into target language. This represents a methodological problem for the article in that using the online Google Translate actually makes their analysis untrustworthy.

 

It’s unfortunate that this paper made it through to publication and it’s a shame that it was (positively) reported on by the New York Times. The paper should either be heavily edited or withdrawn. I’m doubtful that will happen.

 

Update: In the fourth paragraph of this post (the one which starts “On top of that…”), there was some type/token confusion concerning the corpora analyzed. I’ve made some minor edits to it to clear things up. Hat tip to Ben Zimmer on Twitter for pointing this out to me.

Update (March 17, 2015): I wrote a more detailed post (more references, less emoticons) on my problems with the article in question. You can find that here.

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