Which scale format is most commonly used to measure attitudes by asking respondents to indicate their level of agreement (ranging, for example, from 'Strongly Agree' to 'Strongly Disagree')?

Given below are two statements: Statement I: An operational definition translates a vague construct into measurable and observable terms for the purpose of a specific research study. Statement II: A moderator variable is a type of extraneous variable that the researcher fails to control, thereby providing an alternative explanation for the results. In the light of the above statements, choose the correct answer from the options given below:

The variable manipulated by the experimenter in an experiment is called the ________ variable.