In an experiment, the independent variable is best described as:

• A. A variable that is not included in the experimental design
• B. The outcome that is measured in response to changes
• C. A variable that is kept constant throughout the experiment
• D. The factor that is intentionally manipulated by the researcher

Answer: (D)

Verified step by step guidance

1. Understand the definition of an independent variable: It is the factor that the researcher intentionally changes or manipulates in an experiment to observe its effect on the dependent variable.
2. Differentiate between the independent variable and other variables: The dependent variable is the outcome being measured, while controlled variables are kept constant to ensure a fair test.
3. Analyze the options provided: Eliminate choices that do not align with the definition of an independent variable. For example, a variable that is not included in the experimental design cannot be the independent variable.
4. Focus on the correct description: The independent variable is the factor that is intentionally manipulated by the researcher to test its effect on the dependent variable.
5. Conclude that the correct answer is: 'The factor that is intentionally manipulated by the researcher,' as it matches the definition of an independent variable.