Addressing “addressing age-related bias in sentiment analysis”

Posted on February 19, 2018 Updated on February 19, 2018

Algorithmic bias is one of the hot topics of research at the moment. There are observations of trained machine learning models that display sexism. For instance, the paper “Man is to Computer Programmer as Woman is to Homemaker? Debiasing Word Embeddings” (Scholia entry) neatly shows one example in its title with bias in word embeddings, –  shallow machine learning models trained on a large corpus of text.

A recent report investigated ageism bias in a range of sentiment analysis method, including my AFINN word list: “Addressing age-related bias in sentiment analysis” (Scholia entry). The researchers scraped sentences from blog posts and extracted those sentences with the word “old” and excluded the sentences where the word did not refer to the age of the person. They then replaced “old” with the word “young” (apparently also “older” and “oldest” was considered somehow). The example sentences they ended up with were, e.g., “It also upsets me when I realize that society expects this from old people” and “It also upsets me when I realize that society expects this from young people”. These sentences (242 in total) were submitted to 15 sentiment analysis tools and statistics was made “using multinomial log-linear regressions (via the R package nnet […])”.

I was happy to see that my AFINN was the only one in Table 4 surviving the test for all regression coefficients being non-significant. However, Table 5 with implicit age analysis showed some bias in my word list.

But after a bit of thought I wondered why there could be any kind of bias in my word list. The paper list an exponentiated intercept coefficient to be 0.733 with a 95%-confidence interval from 0.468 to 1.149 for AFINN. But if I examine what my afinn Python package reports about the words “old”, “older”, “oldest”, “young”, “younger” and “youngest”, I get all zeros, i.e., these words are not scored to be either positive or negative:

>>> from afinn import Afinn
>>> afinn = Afinn()
>>> afinn.score('old')
0.0
>>> afinn.score('older')
0.0
>>> afinn.score('oldest')
0.0
>>> afinn.score('young')
0.0
>>> afinn.score('younger')
0.0
>>> afinn.score('youngest')
0.0

It is thus strange why there can be any form a bias – even non-significant. For instance, for the two example sentences “It also upsets me when I realize that society expects this from old people” and “It also upsets me when I realize that society expects this from young people” my afinn Python package scores them both with the sentiment -2. This value comes solely from the word “upsets”. There can be no difference between any of the sentences when you exchange the word “old” with “young”.

In their implicit analysis of bias where they use a word embedding, there could possibly creep some bias in somewhere with my word list, although it is not clear for me how this happens.

The question is then what happens in the analysis. Does the multinomial log-linear regression give a questionable result? Could it be that I misunderstand a fundamental aspect of the paper? While som data seem to be available here, I cannot identify the specific sentences they used in the analysis.