Scientific Investigations
Scientific Investigations
A scientific investigation begins with a question and a hypothesis that can be tested. You must know the difference between a hypothesis (a testable prediction) and a theory (a well-supported explanation). Variables matter: the independent variable is what you change, the dependent variable is what you measure, and controlled variables are kept constant to ensure a fair test. A control group provides a baseline for comparison. Reliability improves with repeated trials; validity depends on whether the experiment measures what it claims to measure.
Traps: Students often confuse reliability with validity. Reliability is about consistency; validity is about accuracy. Another trap is thinking a hypothesis is proven; it is only supported or refuted. Also, be careful with sample size and random sampling; small samples reduce reliability.
Worked example: A student tests whether fertilizer affects plant growth. They use three plants with fertilizer and three without, all same species, same light, same water. The independent variable is fertilizer amount; dependent is plant height; controlled variables include light and water. The control group is the plants without fertilizer. To improve reliability, repeat with more plants.
Rule of thumb: For a fair test, change only one variable at a time and keep everything else constant.
Key points
- Hypothesis vs theory
- Independent, dependent, controlled variables
- Control group and experimental group
- Reliability vs validity
- Fair test: one variable changed