A researcher recruited office employees to participate in a study on workplace energy levels.

Each employee wore a smart fitness band to work for two weeks. Every morning, they checked the device's companion app, which displayed a 'daily physical readiness score' (out of 100). The researcher had manipulated these scores so that for seven random days of the study, the app showed high scores (80–95), and for the remaining seven days, it showed low scores (35–50), regardless of the employees' actual sleep or activity.

At the end of each workday, participants completed a brief survey rating their subjective mental fatigue on a scale from 1 to 10. Otherwise, employees went about their usual daily work routines in their normal workplace environment.

Which of the following best describes the experimental method used in this study?