Science and Engineering Practices
What you must understand
This domain tests how scientists and engineers work, not just facts. Know how to write a testable question, identify variables (independent, dependent, controlled), design a fair test, and interpret data in tables and graphs. Understand the difference between an observation and an inference, and between a hypothesis and a conclusion. Know that repeated trials and larger samples improve reliability, and that evidence must support a claim. For engineering, understand the design cycle: define the problem, brainstorm solutions, build a prototype, test it, and improve it based on results. Know how to evaluate whether a design meets criteria and constraints.
Traps to watch for
- Correlation is not causation. Two things changing together does not prove one causes the other.
- Changing more than one variable makes an experiment unfair, so results cannot be trusted.
- Inference is not observation. "The plant wilted" is an observation; "the plant needs water" is an inference.
- A hypothesis is not a guess without reason. It must be testable and based on prior knowledge.
- Engineering constraints are not optional. Cost, time, and materials limit designs.
Rule of thumb
For any experiment question, ask: What is being changed, what is being measured, and what is being kept the same? That answers most variable questions.
Worked example
A student tests whether fertilizer affects plant height. She uses three pots with different fertilizer amounts and measures height after two weeks. The fertilizer amount is the independent variable, plant height is the dependent variable, and water, soil, and light must be controlled.