Run an open investigation
Turn a real problem into a testable question, a plan, and a hypothesis you can actually check.
- Independent vs. dependent variable: A testable question names what you change and what you measure, so you must be able to tell the two apart.
- Choosing a measurable outcome: A question is only testable if its answer is something you can measure with a tool or count.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Run an investigation in order: a testable question, a plan that names the variables, then a hypothesis that predicts the result.
A team tests whether a carbon filter lowers the lead level of tap water. They run the same water unfiltered and filtered, then measure lead in ppb. What is the dependent variable?
Reviewed- A.Whether the water is filtered or not
- B.The lead level (ppb) they measure
- C.The volume of water used
- D.The brand of the filter
Show the worked solution ▾
Answer: B. The lead level (ppb) they measure
- Step 1: Find what they changed: They changed one thing on purpose: filtered vs. unfiltered. That is the independent variable.
- Step 2: Find what they measured: The dependent variable is the outcome they measure in response: the lead level in ppb.
Why it's right: The dependent variable is the measured outcome, which here is the lead concentration in ppb.
- A: Filtered vs. unfiltered is the independent variable: the thing they changed.
- C: Water volume is kept the same, so it is a controlled variable.
- D: Filter brand is held constant here, so it is not the measured outcome.
Aligned to HBS investigation: variables · reading level ~grade 9
- Before sampling, a team writes the question, lists independent/dependent/controlled variables, and a hypothesis: that is the investigation plan.
Fill these in as you work through the lesson.
- Testable question (you answer it by measuring, not by opinion):
- Hypothesis (a prediction you can check):
- Independent variable (the one thing you change on purpose):
- Dependent variable (the thing you measure):
- Controlled variable (what you keep the same so it can't confuse the result):
A question is testable only if its answer is something you can . The hypothesis predicts how the variable will respond when you change the variable.
- Rewrite 'Is lead bad for you?' as a testable question about a measurement.
- For a study soaking water filters in lead solution, name the independent and dependent variables.
- Why must a hypothesis make a prediction instead of just asking a question?
A team worries that an old building's tap water carries too much lead. Write one testable question, name what they would change and what they would measure, and write a hypothesis that predicts the result.