Recognize sources of error, limitations, and the need for replication at a conceptual level.
One result is not always a reliable pattern. Replication helps separate a real effect from random variation or measurement error.
Core Idea
Replication strengthens confidence because single trials can be distorted by chance differences, measurement noise, or an unusual sample.
Understanding
ACT Science often asks why an experiment is limited, not because the setup is useless, but because the evidence is still thin.
- Random variation: one sample may behave unusually.
- Measurement error: a single reading may be off.
- Replication: repeated trials show whether the pattern holds.
A limited experiment can still suggest an answer, but it may not justify a strong conclusion.
Step by Step
- Look for thin evidence: one trial, one sample, or one measurement per condition.
- Ask what could vary by chance: individual differences, timing, or measurement noise.
- Choose the fix that improves reliability: repeat trials or increase the number of samples.
Misconceptions
- Trap: Thinking a bigger effect automatically means the experiment was reliable.
- Trap: Suggesting more variables should be changed at once instead of improving replication.
Worked Example
Students tested whether a new lamp increased algae growth. They placed 1 flask under the new lamp and 1 flask under a standard lamp for 4 days. Both flasks contained the same species of algae, the same nutrient solution volume, and were kept at the same temperature. Algae mass was measured at the end of the 4 days. Which concern most directly limits confidence in the conclusion?
Select an answer to see the explanation