The phrase "are strongly believed" is correct and usable in written English.
It can be used when expressing a widely held opinion or belief about a particular subject or situation.
Example: "These theories are strongly believed to be true by many experts in the field."
Alternatives: "are widely regarded" or "are generally thought".
Temperature, pressure and fluid characteristics are strongly believed to have an effect on wettability (Alotaibi et al. 2010).
Among the cases that are strongly believed to have been deliberate are the EgyptAir crash in October 1999 and a flight between Mozambique and Angola in November 2013.
A further two are strongly believed to be infinite and one remains unsolved.
Several genes including reelin (RELN), glutamic acid decarboxylase 67 (GAD67), and disabled-1 (DAB-1) are strongly believed to be involved in the pathophysiology of SZ.
Remember, for those who are strongly believing in their religion, they might get upset or they might not want to talk to you no more.
It was strongly believed in Lagos that Ojukwu's own sizeable ego was now a factor, and that another leader might have managed to avoid secession.
By the time of the visit he was strongly believed by western counter-terrorism officials to be a senior Isis figure involved in assisting attacks against European targets.
He was subjected to a financial investigation after it was strongly believed that he had hidden assets and had tried to pass £40m in Swiss francs through a Jersey bank account.
It is strongly believed, for example, that Guy Bennett, an art advisor acting on behalf of the Qataris, negotiated third-party guarantees on the top lots at both Christie's and Sotheby's recent contemporary auctions in New York.
It is strongly believed that when he was asked to do the job, he insisted on several conditions, one being that the captain was no longer a selector, and the other was that he could bring his own support staff in where he thought necessary.
