Final answer:
The study described is an experimental study because the independent variable, which is bed angle, is being manipulated by the researcher to observe its effect on the dependent variable, the patients' heart rate.
Step-by-step explanation:
The scenario described by the student, in which a researcher is investigating the effect of bed angle on a patient's heart rate, is an example of an experimental study. In an experimental study, researchers manipulate the independent variable to observe its effect on the dependent variable, which in this case is the patient's heart rate. These levels of bed angle (15°, 30°, 45°) are systematically varied by the researcher to examine the effect on the heart rate, thus making it a controlled environment where the researcher is actively changing the conditions.