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).

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

🧠 Main Subtypes of Prospective Observational Studies

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.

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.

3. Prospective Case Series

Descriptive follow-up of similar patients.
No comparison group.
Example: Series of patients undergoing awake craniotomy.

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.

5. Prospective Longitudinal Study

Repeated measures over time.
Focus on temporal evolution (e.g., function, biomarkers).
Example: Tracking cognition for 12 months after surgery.

📊 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