Science · Scientific investigation
Experimental Design and the Scientific Method
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- A hypothesis must be testable.
- The independent variable is changed by the researcher.
- The dependent variable is measured.
- Controlled variables are kept the same.
- A control group gives a comparison.
- Replication and good sampling strengthen evidence.
What you’ll be able to do
- Write a testable hypothesis.
- Identify independent, dependent, and controlled variables.
- Explain why controls, sampling, and replication matter.
- Tell validity from reliability.
Turn a question into a fair test by choosing variables, controls, samples, and repeated trials.
Optional review
If you’d like to review the basics, visit Scientific Measurement, Units, and Tools. You can start this lesson without completing those first.
From question to testable prediction
Science starts with an answerable question. A hypothesis is a testable proposed explanation or prediction. It should connect a change to a measurable result.
Example: “If light time increases, then bean plants will grow taller over two weeks.” This can be tested. “Plants like light” is too vague because “like” is not clearly measurable.
A hypothesis must be able to be supported or rejected with evidence. It is not a final proven fact. A prediction states the expected result if the hypothesis is correct.
Scientific explanations are tested and revised
A hypothesis is an explanation you can test. A prediction says what you expect to observe. Results may support the explanation or show it needs changing. One successful test does not prove it is always true. A theory explains; a law describes a pattern. A theory does not grow into a law.
Scientific explanations are tested and revised — OpenStax College, Chemistry (CC BY archive). CC BY 3.0. Original source image reproduced unchanged; explanatory caption added.
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