After researching the possible effects of music, Elaina proposes that if people listen to faster-paced music, their pulse rates will increase more than if they listen to slower music. Her mother listens to classic rock at a high volume for 30 minutes, her younger brother listens to classical music quietly while he sleeps at night, and her grandmother listens to two hours of rap at a medium volume. Elaina records each person's pulse before and after listening to the music. What is missing from Elaina's scientific investigation?

A testable hypothesis naming independent and dependent variables
An experiment that takes initial and final measurements
Controlled variables with only one varied independent variable
Experimental data that can be recorded and analyzed