Ruben wants to determine if listening to different types of music will have an effect on a person’s pulse. His hypothesis states that if people listen to rap music, their pulse will increase more than if they listen to other types of music. Ruben takes each participant’s pulse before, during, and after listening to 30 minutes of music. He has his mother listen to rock music, his sister listen to classical music, and his friend listen to rap music. From the data collected, he determined that rap music raises a person’s pulse the most. 1. Identify the independent and dependent variables in Ruben’s hypothesis. 2.Despite the results, this experiment is not able to support Ruben’s hypothesis. Suggest specific improvements that will make the experiment test the given hypothesis. Explain why these changes are improvements.

In any scientific experiment, the independent variable is the one the experimenter changes. The dependent variable is the one measured in order to see if the hypothesis is supported or not. All other conditions (the controlled variables) should remain as identical as possible to make sure the independent variable is the only thing being tested.
1. In Ruben's experiment, his independent variable is the type of music being played, and his dependent variable is the subjects' heart rate.
2. Although it would appear at first glance that Ruben's hypothesis is supported, he did not adequately control his experiment.
He tested only one kind of music on each subject. In order to test his hypothesis, he should test all three types of music on all three subjects, and use the same piece of music for each genre.
His subjects are of different ages, and presumably genders; this could add another variable to Ruben's experiment that needs to be controlled.
Ruben did not note whether his subjects are doing anything else besides listening to music. If one subject is jogging while another is sitting still, he has not tested under identical circumstances.
Ruben's time frame may be too long — any initial increase in pulse could go down either a little or a lot over 30 minutes.
Finally, Ruben's sample size is too small. for his experiment to have any meaning, he will have to repeat his experiment — with the controls noted above— with more people.
Changing these aspects of Ruben's experimental procedure will make Ruben's experiment more valid, as he has then instituted better controlled variables, making it more likely that he is only seeing a result as a result of his independent variable — music type.
https://www.colby.edu/biology/BI17x/expt_method.html

https://www.thoughtco.com/independent-and-dependent-variables-differences-606115