Tweets related to the Black Lives Matter movement suggest that sadness, rather than anger, might be more effective in galvanising people into action, according to new research.

Scientists analysed the emotions behind almost 29 million tweets about four events in 2014 and 2015 that led to Black Lives Matter (BLM) protests in an attempt to identify patterns.

Tweets with a higher level of "negative effect" and sadness, but lower on anger and anxiety were associated with larger rallies the following day, researchers at the Georgia Institute of Technology and the Qatar Computing Research Institute (QCRI) said.

Over time, people changed their posting style, using fewer negative references such as "death", instead opting for more social words such as "we" and "us".

Social upheavals fostered a sense of solidarity among those affected, said Georgia Tech's Munmun De Choudhury, who specialises in social media and mental wellbeing.

"Our analysis of Twitter activity immediately preceding BLM protests shows evidence of the same phenomenon," De Choudhury said.

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The posts analysed regarded the shooting of Michael Brown in Ferguson, Missouri in August 2014; the decision not to indict Ferguson policeman Darren Wilson over Brown's death in November 2014; the shooting deaths of two New York City policemen in December 2014; and the death of Freddie Gray while in the custody of Baltimore police in April 2015.

BLM policy agenda

"We did expect the tweet volume to be predictive of protest volume and it was interesting to see that collective emotions play an important role as well," said co-author Ingmar Weber, from QCRI, which is part of the Hamad bin Khalifa University. "However, we can't say that emotions alone lead to bigger protests as there may be numerous other factors causing them."

People from states with historically high rates of police violence against black Americans were more likely to use negative language, such as words relating to death, even if their state was not the scene of protests.

The research comes as the Black Lives Matter movement gathers pace. A coalition of organisers released on Monday an official policy agenda, calling for an end to the "war on black people", reparations, economic justice, community control, political power and investments in their safety.

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"Social media has been critical in the knitting together of a national narrative of police violence and abuse," Keeanga-Yamahtta Taylor, a professor in African American studies at Princeton University, told Al Jazeera.

"Before, these incidents were depicted as isolated and individual. Social media platforms have shown how they are part of a generalised and pervasive pattern of police abuse."

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She added that social media platforms had helped organisers to "overcome distance and geography by putting people in immediate touch with each other".

As protests have gathered steam, though, some critics have called for Black Lives Matter to be designated a "terror group".

A petition created on July 6, signed by 144,000 people, said: "It is time for the [Pentagon] to be consistent in its actions - and just as they rightfully declared [the Islamic State of Iraq and the Levant - ISIL, also known as ISIS] a terror group, they must declare Black Lives Matter a terror group."

The White House later dismissed the petition.

'Rightfully angry'

"There is a concerted effort by police unions and those who seek their approval to discredit a movement that has exposed police violence and abuse as deeply rooted in police culture," said Taylor. "Their aim is to distract from their illegal and immoral behaviour."

Those who support the movement are driven by both anger and sadness, she said.

"People are rightfully angry that paid public servants regularly disregard the rights of black people with impunity and often the blessing of elected officials.  People are sad because innocent men, women and children are being killed unjustly."

At least 633 people have been killed by police in the US so far this year, according to a tally being kept by the Guardian media organisation.

Race will be a key talking point  in the months ahead in the US, as campaigning for the November presidential election intensifies.

At least 156 of the 633 killed were black, according to the Guardian figures.

Follow Anealla Safdar on Twitter: @anealla

Source: Al Jazeera