ACT Science: Scientific Investigation (Research Summaries) — How to Reason Through Experiments

Research Summaries passages

ACT Science passages that describe one or more experiments and figures; they mainly test whether you understand what the researchers did.

Experimental tools

The instruments or materials used to measure or change something in a study, such as balances, thermometers, or pH meters.

Procedures

The step-by-step actions that explain how an experiment was run, including preparation, timing, what changed, and what was measured.

Accuracy

How close a measurement is to the true or accepted value.

Precision

How consistent repeated measurements are with one another.

Resolution

The smallest change an instrument can reliably detect.

Independent variable

The factor the experimenter intentionally changes between groups or trials.

Dependent variable

The outcome that is measured to see how it responds to the independent variable.

Controlled variables

Factors kept the same across all conditions so they do not affect the results.

Control group

The baseline condition used for comparison, often receiving no treatment or a standard treatment.

Confounding variable

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

Experimental design

The overall plan of an experiment, including the question, variables, controls, timing, trials, and data collection.

Replication

Repeating measurements or trials to reduce the impact of random variation and make results more reliable.

Random error

Unpredictable variation between measurements or trials that causes scattered results.

Systematic error

A consistent bias in measurement, such as a miscalibrated instrument, that shifts results in one direction.

Fair test

An experiment in which only one main factor is changed while other relevant factors are kept constant.

Validity

How well a procedure or measurement actually measures what the experiment claims to measure.

Operational definition

The specific way a concept is defined and measured in a particular experiment.

Percent change

A comparison of a new value to an old value, calculated as (new − old) / old × 100%.

Percent error

A comparison of a measured value to an accepted value, calculated as |measured − accepted| / accepted × 100%.

Comparing experiments

Looking for similarities and differences in variables, tools, controls, timing, and procedures across multiple experiments.

Extending experiments

Designing a logical next step, such as adding more levels, widening the range, or adding a control while keeping the method consistent.

Interpolation

Predicting a value within the range of data that has already been tested.

Extrapolation

Predicting a value beyond the tested data range, which is usually less certain.

Mean (average)

The sum of all measurements divided by the number of measurements; it is often the best prediction for a new trial under the same conditions.