Measurement & Experimental Science
Randomization, Blocking & Position Effects
Position in a room, greenhouse, or field can create systematic light, temperature, airflow, soil, and edge effects. Randomization and blocking help keep those gradients from being confused with the treatment being tested.
Key concepts
- Spatial gradients can bias treatment comparisons
- Randomization reduces systematic placement bias
- Blocking groups similar positions before treatment assignment
- Edge plants may behave differently from interior plants
What to measure or observe
- Map the experimental layout
- Identify known gradients
- Randomize within appropriate blocks
- Record plant moves or replacements
Common mistakes
- Putting all treatment plants under one fixture and controls under another
- Ignoring greenhouse bench position
- Replacing failed plants without preserving treatment records
- Using only edge plants for one group
Visuals this lesson still needs
- Biased-versus-randomized layout
- Blocked greenhouse bench example
- Field gradient diagram
- Edge-effect map