A controlled experiment is one that
a. Proceeds slowly enough that a scientist can make careful records of the results.
b. Keeps all variables constant.
c. Is repeated many times to make sure the results are accurate.
d. Tests experimental and control groups in parallel.

Verified step by step guidance

1. Understand the definition of a controlled experiment: A controlled experiment is a scientific test where the researcher manipulates one variable (independent variable) while keeping all other variables constant to observe its effect on the dependent variable.
2. Identify the key components of a controlled experiment: It involves an experimental group (where the independent variable is altered) and a control group (where the independent variable is not altered). These groups are tested in parallel to compare results.
3. Analyze the options provided in the question: Option (a) refers to the speed of the experiment, which is not a defining feature of a controlled experiment. Option (b) suggests keeping all variables constant, which is incorrect because the independent variable is intentionally changed. Option (c) refers to repetition for accuracy, which is a good practice but not specific to controlled experiments. Option (d) correctly describes the parallel testing of experimental and control groups.
4. Eliminate incorrect options based on the analysis: Options (a), (b), and (c) do not align with the definition of a controlled experiment, leaving option (d) as the correct choice.
5. Conclude that the correct answer is option (d), as it accurately describes the testing of experimental and control groups in parallel, which is a hallmark of a controlled experiment.

Key Concepts

Controlled Experiment

A controlled experiment is a scientific test that aims to isolate the effect of a single variable by keeping all other variables constant. This allows researchers to determine the causal relationship between the independent variable (the one being tested) and the dependent variable (the one being measured). By controlling extraneous factors, scientists can draw more reliable conclusions from their data.

Variables in Experiments

In the context of experiments, variables are elements that can change or be manipulated. The independent variable is the factor that is altered to observe its effect, while the dependent variable is the outcome that is measured. Control variables are those that are kept constant to ensure that any changes in the dependent variable are solely due to the manipulation of the independent variable.

Experimental and Control Groups

In a controlled experiment, the experimental group receives the treatment or condition being tested, while the control group does not. This comparison allows researchers to assess the effect of the independent variable by observing differences in outcomes between the two groups. Testing both groups in parallel ensures that results are not influenced by external factors, enhancing the validity of the findings.