====== Prospective observational study ======

An [[observational study]], often [[longitudinal]] in nature, for which the consequential outcomes of interest occur after study commencement (including the creation of a study protocol and analysis plan, and study initiation).

===== Classification =====

Prospective observational studies collect data **forward in time** without intervening. They are a key design for real-world clinical research.

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==== 🧠 Main Subtypes of Prospective Observational Studies ====

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=== 1. Prospective Cohort Study ===
  * Follows a defined group (**[[cohort]]**) over time.
  * Groups may be based on exposure or risk.
  * Outcomes are observed without intervention.
  * Example: 100 elderly patients undergoing neurosurgery for brain metastases, followed for complications.
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=== 2. Registry-Based Prospective Study ===
  * Data collected through **multi-institutional registries**.
  * Reflects real-world practice.
  * May include various exposures and outcomes.
  * Example: Registry of CNS metastases patients receiving different treatments.
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=== 3. Prospective Case Series ===
  * Descriptive follow-up of similar patients.
  * No comparison group.
  * Example: Series of patients undergoing awake craniotomy.
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=== 4. Prospective Case-Control Study ===
  * Participants selected based on **future outcomes**.
  * Past exposures compared retrospectively.
  * Often nested within a cohort.
  * Example: Patients who develop radiation necrosis vs. those who don’t.
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=== 5. Prospective Longitudinal Study ===
  * Repeated measures over time.
  * Focus on temporal evolution (e.g., function, biomarkers).
  * Example: Tracking cognition for 12 months after surgery.
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==== 📊 Summary Table ====

^ Subtype                      ^ Groups Compared? ^ Outcome Over Time? ^ Intervention? ^ Typical Use                          ^
| [[Prospective Cohort study]]         | Yes              | Yes                | No            | Exposure-outcome analysis           |
| [[Registry-Based study]]           | Optional          | Yes                | No            | Real-world multicenter data         |
| Prospective Case Series     | No               | Yes                | No            | Descriptive outcomes                |
| Prospective Case-Control    | Yes              | Retro from outcome | No            | Risk factors (nested case-control)  |
| [[Prospective Longitudinal study]]    | No/Optional       | Yes (repeated)     | No            | Tracking change over time           |