Overview
This lecture explains pseudoreplication in experimental design, why independent replication is critical, and how to avoid common pitfalls in sampling and analysis.
Importance of Replication
- Replication improves the reliability of experimental results by sampling more subjects or repeating experiments on different subjects.
- Independent measurements are necessary to accurately estimate population variation.
Pseudoreplication Explained
- Pseudoreplication occurs when repeated measurements are taken from the same subject or non-independent sources, giving a false sense of replication.
- Measuring the same individuals multiple times does not increase the sample size meaningfully.
- Using samples from the same location or group (e.g., animals from one facility) may not provide true replication.
Common Sources of Pseudoreplication
- Shared environments, such as mice in the same cage or people in the same household, can introduce common factors that bias results.
- Environmental factors like region, pollution, or climate may affect all subjects similarly and confound results.
- Genetic similarity (e.g., animals from the same parents) can skew experimental findings.
- Timing issues, like conducting experiments at the same time of day or year, can limit independence.
Solutions and Best Practices
- Problems of pseudoreplication cannot be fixed by statistics alone; subject matter experts are needed to identify risks.
- Design experiments to include subjects from different genetic backgrounds, environments, and times.
- In human studies, ensure diversity in race, socioeconomic status, gender, age, health, and geography.
- Always identify and acknowledge possible sources of pseudoreplication, even if they cannot be avoided completely.
Key Terms & Definitions
- Replication — Repeating experiments or measurements to estimate the true effect more accurately.
- Pseudoreplication — Pretending to have independent replicates when samples or measurements are not truly independent.
- Independent Measurements — Data collected from subjects or conditions unaffected by each other.
Action Items / Next Steps
- Review your experimental design for possible sources of pseudoreplication.
- Consult experts to identify and address hidden dependencies in samples.
- Ensure sampling strategies include adequate diversity and independence.