1. What is Retention Rate?

Retention rate measures the percentage of participants who remain in a study over time. It's a key metric in research to assess participant engagement and study quality.

2. How Does the Calculator Work?

The calculator uses the retention rate formula:

Where:

• Participants Retained — Number of participants who completed the study or remained at follow-up
• Participants Started — Initial number of participants enrolled in the study

Explanation: The formula calculates what percentage of the original study population was retained through the study period.

3. Importance of Retention Rate

Details: High retention rates are critical for study validity. Low retention can introduce bias and reduce statistical power. Most clinical trials aim for ≥80% retention.

4. Using the Calculator

Tips: Enter whole numbers for participants retained and started. The started number must be greater than zero, and retained cannot exceed started.

5. Frequently Asked Questions (FAQ)

Q1: What's a good retention rate for research studies?
A: Ideal rates vary by study type and duration, but generally ≥80% is good, ≥90% is excellent for most clinical research.

Q2: How does retention rate differ from completion rate?
A: Retention rate counts participants still in study (even if not completed all procedures), while completion rate counts those who finished all study requirements.

Q3: What strategies improve retention?
A: Regular contact, reminder systems, minimizing burden, compensation, and building rapport all help improve retention.

Q4: Should I report retention rate by study arm?
A: Yes, it's important to report retention by study group as differential attrition can affect results.

Q5: How should missing data be handled?
A: Intention-to-treat analysis typically counts dropouts as non-responders, while per-protocol analysis excludes them.