For DIY quantification, create a spreadsheet of userids, threads and manually tagged perspectives from your favorite social network or discussion forum. Then apply open-source tools for social network graph analysis of node interactions. With this data, apply exclusion filters to targeted clusters of userids, then re-read the "mass opinion". Palantir has proprietary software for network influence analysis, but many algorithms and OSS tools are available from academia.
On one hand, it's the 'Big Lie': People naturally doubt such deception is occurring until they see a smoking gun, and even then many deny it.
On the other, it is such an obvious, inexpensive way to drive public opinion, I'd be shocked if it wasn't widely used. Even paying U.S. minimum wage, you probably are paying under 50 cents/post. That's 10,000 comments in your favor for < $5K -- without knowing data on the influence of such things, it seems cost-effective compared to advertising. Imagine a local politician or a super-PAC doing it before an election in just one locality.
Also interesting: Many people I know think they can detect astroturfing when they see it. I'm sure that's true sometimes, but the astroturfers have more experience and are more sophisticated in their craft than we are -- they do it all day, every day. They know what makes something look credible, and you can see that discussed in the article.
EDIT: I just found this:
Grassroots for Hire: Public Affairs Consultants in American Democracy by Edward T. Walker
Although 'grassroots' conjures up images of independent citizen organizing, much mass participation today is sponsored by elite consultants working for corporations and powerful interest groups. This book pulls back the curtain to reveal a lucrative industry of consulting firms that incentivize public activism as a marketable service. Edward Walker illustrates how, spurred by the post-sixties advocacy explosion and rising business political engagement, elite consultants have deployed new technologies to commercialize mass participation. Using evidence from interviews, surveys and public records, Grassroots for Hire paints a detailed portrait of these consultants and their clients. Today, Fortune 500 firms hire them to counter-mobilize against regulation, protest or controversy. Ironically, some advocacy groups now outsource organizing to them. Walker also finds that consultants are reshaping both participation and policymaking, but unethical 'astroturf' strategies are often ineffective. This pathbreaking book calls for a rethinking of interactions between corporations, advocacy groups, and elites in politics.
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