When looking at Twitter's trends one can find trends with hashtags:
But also without it:
- Patrick Kane
Why are there trends without a hashtag?
How are they created?
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Hashtags are a self-selected marker, but considering all of the data they have available they have tons of information about what people are tweeting about at any given time. As long as they can identify something as an actual "topic" and not just a couple of words that are adjacent in a sentence, this would be a candidate to be trending.
The algorithm behind this is part of Twitter's "secret sauce". They're not going to share the details because it's a competitive advantage and to prevent people manipulating the list for their own gain. They already have "social media consultants" trying to game the system so that their clients tweets end up on the list. If the details were known, it would quickly become useless. Twitter also has rules against this sort of thing:
Are there rules for trends?
Yes, and we outline them in the Twitter Rules because it is possible to abuse trends. The following behavior could cause your account to be filtered from search or even suspended:
- Adding one or more topics/hashtags to an unrelated Tweet in an attempt to gain attention in search.
- Repeatedly Tweeting the same topic/hashtag without adding value to the conversation in an attempt to get the topic trending or trending higher.
- Tweeting about each trend in order to drive traffic to your profile or website, especially when mixed with advertising.
- Listing trends in combination with a request to be followed.
- Tweeting about a trend and posting a misleading link to something unrelated.
A Twitter engineer, but one that doesn't work on Trends, says that the process is essentially:
- extract terms (hashtags, phrases, words etc)
- remove spammy, trashy, offensive terms
- compare the current frequency of those terms to the historical frequency (we're looking for novelty, not popularity) (I don't know what we use, but you could use something like TF/IDF or even simpler)
- sort them by novelty
The Official Twitter FAQ says:
How are trends determined?
Trends are determined by an algorithm and, by default, are tailored for you based on who you follow and your location. This algorithm identifies topics that are popular now, rather than topics that have been popular for a while or on a daily basis, to help you discover the hottest emerging topics of discussion on Twitter that matter most to you.