Scientific Inquiry and Process Skills: Fair Tests and Evidence
What to know
Scientific inquiry starts with a question and a testable prediction, or hypothesis. A fair test changes one independent variable, measures one dependent variable, and holds everything else constant as controlled variables. Observations are what you detect with senses or instruments; inferences are explanations built on those observations, and they can be wrong. Measurements need both a number and a unit, along with attention to precision and accuracy.
Data belong in tables and graphs: line graphs show change over continuous time, bar graphs compare categories, and every graph needs labeled axes and a title. Conclusions should be limited to what the data actually support. Repeating trials and increasing sample size improve reliability; a single result is weak evidence. Models represent things too big, small, fast, or slow to observe directly, and every model has limits. A scientific theory is a well-supported explanation, not a guess.
Traps to watch
Questions often hide a second changed variable, making the test unfair. Watch for correlation presented as causation, conclusions that reach beyond the data, and options claiming a hypothesis has been "proven." Also check whether a question asks for an observation (what happened) or an inference (why it happened).
Worked example
A student waters three identical plants with 0 mL, 50 mL, and 100 mL of water and measures height after two weeks. Independent variable: amount of water. Dependent variable: plant height. Controlled variables: plant type, pot size, soil, light, and time. Rule of thumb: change one thing, measure one thing, and keep everything else the same.