ACT Science Reasoning: Evaluating Evidence, Models, and Conclusions

Validity

How trustworthy and well-supported a scientific claim is based on the evidence and methods used.

Correlation

A relationship in which two variables change together.

Causation

A relationship in which changing one variable produces a change in another variable.

Controlled experiment

A study design in which one variable is intentionally changed while other factors are kept the same to test cause-and-effect more clearly.

Observational pattern

A pattern seen in data when no variable is manipulated; it can show an association or trend but usually not causation.

Confounding variable

An extra factor that changes along with the tested variable, making it unclear what actually caused the result.

Bias

A systematic influence that pushes results in one direction.

Measurement error

Random or systematic inaccuracy in the readings or data collected.

Small sample size

A situation with too few trials or subjects to make the results strongly convincing, especially if the data are noisy.

Control or baseline

A comparison condition used to judge whether a measured change is meaningful.

Independent variable

The factor that is intentionally changed or tested in an experiment.

Dependent variable

The factor that is measured to see how it responds to changes in the independent variable.

Conclusion

A claim that summarizes what the data imply.

Interpolation

Estimating a value within the range of data that was actually tested.

Extrapolation

Predicting a value beyond the tested range of the data.

Prediction

A claim about an unmeasured case or future observation based on a pattern in the data.

Linear trend

A pattern in which roughly equal changes in x produce roughly equal changes in y.

Inverse trend

A pattern in which y decreases as x increases.

Plateau

A pattern in which a value increases at first and then levels off with little further change.

Optimum curve

A pattern in which a value rises to a maximum point and then decreases.

Model

A simplified representation or explanation of how a system works.

Hypothesis

A testable proposed explanation or prediction.

Competing models

Different explanations or hypotheses for the same phenomenon that must be compared against the evidence.

Inference

A logical interpretation that goes beyond simply restating the data.

Supported inference

An interpretation that is justified by specific data, matches the observed trend, and stays within the tested conditions.