--- title: "Clinical Trials: Phases, Endpoints and Why Most Candidates Fail" description: "Trial design decides what a result is allowed to claim: which patients, which comparator, which endpoint measured when. This stop reads a protocol and locates the point at which most candidates stop." canonical: https://lightmysky.com/learn/science/clinical-trials-phases-endpoints-and-why-most-candidates-fail-mt_xKBKzSYxLh source: https://lightmysky.com/learn/science/clinical-trials-phases-endpoints-and-why-most-candidates-fail-mt_xKBKzSYxLh.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Clinical Trials: Phases, Endpoints and Why Most Candidates Fail Trial design decides what a result is allowed to claim: which patients, which comparator, which endpoint measured when. This stop reads a protocol and locates the point at which most candidates stop. Subject: Science · Area: The Human Body · Ages 23 to 24 Page: https://lightmysky.com/learn/science/clinical-trials-phases-endpoints-and-why-most-candidates-fail-mt_xKBKzSYxLh ## Ready when they can - State what each trial phase is designed to establish, and for which population - Distinguish a surrogate endpoint from a clinical one and say what each can support - Explain why efficacy failures cluster where they do and what that says about target choice ## Lesson: What a trial result is allowed to claim Trial phases climb a ladder of bias resistance. Early phases ask whether the treatment is safe and what dose humans tolerate. Middle phases ask whether it shows activity in patients. Late phases randomize large groups against standard care to prove real benefit. Skipping a rung leaves the next claim standing on hope. Randomization balances even the factors nobody measured, because assignment rather than judgement decides who gets what. Blinding stops expectations from bending treatment, reporting, and scoring. Together they protect the endpoint from everyone involved, including the investigators. **Example.** Results often boil down to comparing event rates between two groups. Relative risk divides the rate on treatment by the rate on control, so below one means fewer events with treatment. A glowing ratio on a stand-in marker supports far less than the same ratio on survival or function, which is the surrogate trap. **Tip.** Read every protocol for consent, fair subject selection, and proportionate risk, since review boards gate each phase on those rails. Then locate where most candidates stop: the step where real benefit must first be shown. Weak validation earlier is what usually surfaces there. **Recap.** Phase, randomization, endpoint type, and ethics decide what the result may claim. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Epidemiology: Incidence, the Reproduction Number and Tracking an Outbreak](https://lightmysky.com/learn/science/epidemiology-incidence-the-reproduction-number-and-tracking-an-outbreak-mt_f2tT08sEki) - [Confidence Intervals for Means and Proportions](https://lightmysky.com/learn/mathematics/confidence-intervals-for-means-and-proportions-mt_Pg2fPDW1sn) - [Target Validation and Lead Discovery: From a Biological Claim to a Molecule](https://lightmysky.com/learn/science/target-validation-and-lead-discovery-from-a-biological-claim-to-a-molecule-mt_xHWq5Rg85r)