Measurement & Experimental Science
Controls, Baselines & Before/After Comparisons
A before/after change in one treated plant does not show what would have happened without the treatment. Controls and baseline measurements provide the comparison needed to interpret change.
Key concepts
- A control represents the comparison condition
- Baseline data show starting differences
- Natural development can create change even without treatment
- Concurrent controls are stronger than memory or historical anecdotes
What to measure or observe
- Define the control before treatment
- Collect the same baseline variables in all groups
- Measure groups on the same schedule
- Record deviations from the planned protocol
Common mistakes
- Calling pre-treatment data the control group
- Comparing this crop with a vague memory of last crop
- Measuring treatment plants more carefully than controls
- Changing control practices midway
Visuals this lesson still needs
- Before-after versus controlled comparison
- Baseline balance table
- Concurrent control timeline
- Protocol deviation log