The policy introduced last year (saying more in fewer words) (C1 Grammar)

Formal and academic writing tightens a noun phrase by cutting which was / which were / that was / that were and keeping just the past participle. The meaning is unchanged, but the sentence is leaner: "the policy that was introduced last year" becomes "the policy introduced last year". The past participle signals the action was done to the thing. Reach for this in reports, essays and news writing, where the density reads as polished; in relaxed speech the fuller "which was introduced" sounds more natural.

Drop "which was": leave the past participle

• The policy that was introduced last year → The policy introduced last year.
• The data which were collected from surveys → The data collected from surveys.
• A report that was published in 2024 → A report published in 2024.
• Not "the policy introducing last year" — say "the policy introduced last year". The policy is introduced by someone — the action is done to it — so keep the past participle introduced, not the -ing form. Use -ing only when the thing itself does the action.
• Try it: the building which was restored after the fire Tighten it: cut "which was" and keep the past participle. (Leave out the word you don't need.) Answer: the building restored after the fire — Cutting which was and keeping the past participle gives the leaner the building restored after the fire. "Which was" is exactly what the tightening removes, so it is left out. The past participle restored already carries the done-to meaning on its own.

Drop "who are": leave the -ing form

When the relative clause already contains is / are + an -ing form, cut who is / who are / that is / that are and keep the -ing form: "students who are preparing for exams" becomes "students preparing for exams". Same meaning, fewer words, a more formal written feel. The is / are has to be there for this to work: "the man who owns the shop" has none, so it stays as it is (not "the man owning the shop"). Notice the split: the -ing form (preparing) says the thing does the action, while the past participle (introduced, collected) says the action is done to it. Like the past participle version, this is a tool of formal and academic prose; keep the full "who are preparing" when you want a plainer, more conversational tone.

• Students who are preparing for exams → Students preparing for exams.
• The team that is leading the project → The team leading the project.
• Visitors who are arriving after six → Visitors arriving after six.
• Not "students prepared for exams" — say "students preparing for exams". The students are doing the preparing, so keep the -ing form preparing. Prepared is the past participle and would mean someone else prepared the students.
• Try it: researchers who are studying the climate Tighten it: cut "who are" and keep the -ing form. (Leave out the word you don't need.) Answer: researchers studying the climate — Cutting who are and keeping the -ing form gives researchers studying the climate. "Who are" is what the tightening removes, so it is left out. The -ing form studying carries the active meaning by itself.

Move it in front: join with a hyphen

Formal, academic and headline writing compresses a phrase that sits after a noun into a single hyphenated piece before it: "a protocol based on evidence" becomes "an evidence-based protocol". The pieces regroup in front of the noun and are joined with a hyphen, giving a punchy, economical phrase that acts as one word. Two things to watch. A measurement word goes singular in front: "a report of 200 pages" becomes "a 200-page report", and "a meeting of three hours" becomes "a three-hour meeting". And the hyphen itself is a matter of house style rather than grammar — publications differ on how many of these they hyphenate — so follow the style guide you are writing for and be consistent. Reach for the whole move when you want density and a formal, written tone; the fuller after-the-noun version stays clearer in relaxed, spoken English.

• a protocol based on evidence → an evidence-based protocol
• a plan for the long term → a long-term plan
• a report of 200 pages → a 200-page report
• Not "an evidence based training protocol" — say "an evidence-based training protocol". In front of the noun the two words act as one, so join them with a hyphen: evidence-based. Without it they read as two loose words.
• Try it: a training protocol based on evidence Move the phrase in front of the noun as one hyphenated piece. (Leave out the word you don't need.) Answer: an evidence-based training protocol — Moved in front of the noun, based on evidence becomes the hyphenated evidence-based: an evidence-based training protocol. "Based on evidence" is the after-the-noun version, the very thing you are reshaping, so it is left out. The pieces flip and join with a hyphen.
• Try it: A committee is going through every application right now. The committee is the one doing the reviewing. Which one fits — the committee that is doing the reviewing? (the committee reviewing the applications / the committee reviewed the applications) Answer: the committee reviewing the applications — The committee is doing the reviewing, so it is active — keep the -ing form: the committee reviewing the applications. "Reviewed" is the past participle and would flip the meaning, saying the committee itself was reviewed by someone else. Use -ing when the thing acts, the past participle when the action is done to it.