Which of the following independent variables cannot be manipulated in a research study?

Gender, ethnicity and inborn traits like intelligence are all independent variables that cannot be manipulated.

These are attribute variables, already fixed in the participant before the study.

Gender is assigned by the participant's existing status and cannot be altered by the researcher.

Ethnicity is a pre-existing characteristic beyond experimental control.

Intelligence and other inborn traits are measured, not created or changed at will.

Such non-manipulable causes are studied through ex post facto or correlational designs.