Question

which of the following statements represents a critical difference between non - experimental and experimental research methods?
○ b) experimental methods involve operational definitions, non - experimental methods do not.
○ c) non - experimental methods involve the manipulation of independent variables and random assignment to conditions; experimental methods do not.
○ d) experimental methods involve the manipulation of the independent variable and random assignment to conditions; non - experimental methods do not.
○ a) non - experimental methods involve operational definitions; experimental methods do not.

Explanation:

• Option A: Both experimental and non - experimental research use operational definitions to define variables clearly, so A is wrong.
• Option B: As mentioned above, both types of research use operational definitions, so B is wrong.
• Option C: The manipulation of independent variables and random assignment to conditions are characteristics of experimental research, not non - experimental. So C has the description reversed and is wrong.
• Option D: Experimental research is defined by the manipulation of the independent variable (to see its effect on the dependent variable) and random assignment (to control for confounding variables). Non - experimental research does not manipulate the independent variable or use random assignment (for example, in correlational or observational studies). So D correctly states the critical difference.

Answer:

D) Experimental methods involve the manipulation of the independent variable and random assignment to conditions; non - experimental methods do not.