とされる

1. 1Is widely regarded as having a certain quality or value, as a commonly held evaluation.Ex. 1
2. 2Is believed or held (by experts or official accounts) to be the case, e.g. dates, origins, or figures.Ex. 2

A formal, written expression typical of news articles, textbooks, academic writing, and official explanations. It attributes a claim to general or authoritative opinion without naming a specific source, which gives the statement an objective, impersonal tone. The forms とされている and とされており are very frequent for established views.

• と考えられるN2「と考えられる」 centers on a judgment reached by reasoning from facts and can express the speaker's own inference. When 「と考えられている」 means 'it is generally thought,' it is basically interchangeable with 「とされる」, but it cannot be used for the sense of being designated as something by rule or regulation.
• ものと思われるN1「ものと思われる」 is the speaker's own tentative conjecture based on materials, whereas 「とされる」 relays the views or presumptions of society and academia and can also mean being designated as having a certain quality by rule or regulation. Because the two differ in standpoint, they should generally not be interchanged.
• ということだN3「ということだ」 relays information heard or read from somewhere; the source can be identified with 「によると」, it is neutral in register, and it can also mean 'in other words.' 「とされる」 relays an accepted view or presumption without identifying who holds the view, is more written in tone, and can also mean 'be designated as.'
• らしいN4「らしい」 is neutral in register and mostly expresses conjecture based on specific hearsay or signs. 「とされる」 is written in tone, relays an accepted view or presumption, and can also mean being designated as a certain quality by rule or regulation — a sense that 「らしい」 cannot replace.
• によると / によればN3「によると」 attaches to nouns and identifies the source of the information; it is usually paired with sentence-final 「そうだ」 or 「らしい」, can also be used for inference based on materials, and works in both speech and writing. 「とされる」 attaches to the plain form or nouns, among others, does not identify its source, and has a strong written-language flavor.

Unlike と考えられる and ものと思われる, which present a reasoned inference or cautious conjecture, とされる reports a view already held by society, experts, or officials. Unlike ということだ, らしい, and によると/によれば, which relay hearsay or mark a specific information source, it states an established view impersonally, without naming who holds it.