We summarize our findings as word-clouds of the 100 most frequent hashtags in the ASD and control data sets in Fig. 6(a) and Fig. 6(b). As in the previous analysis of the most frequently used terms, the difference between the two data sets is readily apparent. Unsur- prisingly, most of the hashtags in the ASD data set pertain to health issues, some of which are ipso facto ASD-related, such as “mentalhealth” and “psychology”, while others are less obviously so. Examples of the latter include “fibromyalgia” and “vaccines”. Fibromyalgia is a class of disorders related to the body’s processing of pain which recent evidence sug- gests may have a potential connection with ASD [40]. Similarly, although now discredited, previous research had suggested a causal link between children being vaccinated and devel- oping autism [41]. These examples are further evidence of the type of powerful information which can be harvested from Twitter. In particular, it shows that it is possible to data-mine tweets to provide feedback to medical practitioners on the concerns of the ASD community, the penetration (or lack thereof) of relevant public health recommendations (e.g. ABA or the applied behaviour analysis), or the adoption of treatments of questionable efficacy (e.g. homeopathy, gluten-free diet). 

Much like the word-cloud in Fig. 5(a), the hashtag word-cloud in Fig. 6(a) contains many references to various topics pertaining to the support of individuals on the autism spectrum. However, the nature of the two sets of terms is somewhat different. While the most fre- quently used terms mostly referred to the issues themselves, the corresponding hashtags mostly refer to particular support groups. For example, “autismspeaks” (centre-left position within the word-cloud) is a US-based autism advocacy organisation, “thisisautism” (centre- right position within the word-cloud) a Twitter stream used to share autism-related experi- enced, and ‘AS2DC’ (top-right corner of the word-cloud) an action summit on autism held in Washington D. C. 

## 4.4.3 Part-of-speech analysis 

In Section 4.4.1, in the discussion of our findings in the comparative analysis of the most frequently used words in the ASD and control tweets, we observed that the ASD tweets appeared to contain a greater proportion of nouns and a smaller proportion of verbs than 

