Pranoti Pimpalkhute (2), Apurv Patki (2), Azadeh Nikfarjam (2), Graciela Gonzalez (1)
(1) Department of Biostatistics, Epidemiology and Informatics
Perelman School of Medicine
University of Pennsylvania
Philadelphia, PA, USA
(2) Department of Biomedical Informatics
Arizona State University
Scottsdale, AZ, USA
Social media postings are rich in information that often remain hidden and inaccessible for automatic extraction due to inherent limitations of the site’s APIs, which mostly limit access via specific keyword-based searches (and limit both the number of keywords and the number of postings that are returned). When mining social media for drug mentions, one of the first problems to solve is how to derive a list of variants of the drug name (common misspellings) that can capture a sufficient number of postings. We present here an approach that filters the potential variants based on the intuition that, faced with the task of writing an unfamiliar, complex word (the drug name), users will tend to revert to phonetic spelling, and we thus give preference to variants that reflect the phonemes of the correct spelling. The algorithm allowed us to capture 50.4 – 56.0 % of the user comments using only about 18% of the variants.
Considering the possible ways the misspellings may occur in drug names, we sought to develop an algorithm to generate a list of all the likely misspelled variants of a drug name based on a simple 1-edit distance algorithm, and then filtering it using phonetic spelling. We evaluated the approach as to its ability to generate a list with maximum coverage of social networking postings for a minimum list size.
We used four drugs for the purpose of experiments. In order to evaluate our proposed approach, we want to compute the fraction of useful posts that the method was able to capture from the crawling API using the variants generated by the algorithm. Since it is not possible to retrieve the exact number of posts corresponding to a variant from the API due to its limitations, we retrieved the comments using screen scraping in order to get a true measure of misspelled variants.
In this evaluation strategy we compared the results of our algorithm to a random keyword selector which is our baseline. We show that our algorithm produces a significant improvement over random keyword selector. The essence of our method is to capture a large amount of relevant data from a small variant list.
Figure 2 show the plots for number of comments obtained from Twitter vs the number of drug variants. The X-axis represents the combined list of drug variants obtained from the CMU pronunciation and the Metaphone library and the Y-axis represents the Google hits for the variant. The drug variants were ranked according to the Google hits obtained from the custom search API. It is evident from Figure 2 that total number of comments does not increase by much after a particular point. The algorithm allowed us to capture 50.42 – 55.97% of comments using about 18.29% of the variants.
Figure 3 shows that our method has an advantage when the keyword coverage is less, and that the method can capture useful data with minimal keyword coverage. For instance, for 20% keyword coverage the random selector captured 32 tweets while our approach captured 170 tweets for Seroquel.
Our work focuses on finding a balance between the restrictions imposed by the crawling APIs and the many variants of a drug name needed to capture the large amount of data that hides behind these restrictions. Other approaches seek to correct misspelling by mapping the drug names from free text to standard nomenclature(13), but given the context of this work, these methods will fail in extracting data from social media given that all the data cannot be captured beforehand and then filtered out.
The main limitation of this algorithm is that some common misspellings that are due to typographical errors could be missed and might be commonly used. The false negative rate cannot be adequately computed since the universal set is not known. Moreover, the data obtained from social networking sites is complicated. For example, for the word Prozac, there are tweets that are not related to the drug “Local woodstock continues After the wild cats and a live connection with Ibiza now are the prozec mckenzie on stage … Tonight only”. The keyword coverage can be manipulated to achieve a higher comment coverage, adjustin for the number of drugs to track and API limits. Moreover, it is important to appreciate that crawling API is a resource which can be used in a better way if we have tracking words that are relevant.