The phrase "are mostly held" is correct and usable in written English.
It can be used to describe events, meetings, or items that are primarily conducted or located in a certain way or place.
Example: "The annual conferences are mostly held in the spring to accommodate the schedules of the participants."
Alternatives: "are primarily conducted" or "are mainly organized".
Jazz and every other musical genre wafted though the warm night air, although finding live events was a challenge, since they are mostly held in pricey indoor venues.
The highest-cost end of those businesses, the trade shows and exhibitions that are mostly held in convention centers in 15 or 20 major cities, is still reeling.
"She was continually challenging the boundaries of genre," said Marta Werner, a professor at D'Youville College in Buffalo and the creator of "Radical Scatters," a 1999 digital project based on the scraps, which are mostly held by Amherst.
In addition, when ballot votes regularly do not take place in conjunction with general elections (like in Switzerland), turnout variation will be stronger than when referendum votes are mostly held on election days (like in the United States).
These same families are likely to be those worst affected by the planned national minimum wage: low-paid jobs, which a minimum wage might destroy, are mostly held by women.So much for accidental incentives to stay at home.
Mr von Freyberg set about instituting checks on the bank's 19,000 accounts, which are mostly held by Vatican employees, charities, priests and nuns.
Newspapers are under pressure to do the same, but are mostly holding out.
Real estate agents with whom I have commiserated on the difficulty of finding a home for their buyers are mostly holding their cards close to their chest.
And for those remaining private, capital continues to flow in while disclosed valuations are mostly holding up.
Leasing commercial space in San Francisco is as expensive as ever, but prices are mostly holding steady for the first time in a long time — not rising.
Shares endured a 3% hit last week, but investors are mostly holding on — even though the company hasn't outlined when and how it can return to robust growth.
