Answer: Correlational design
Step-by-step explanation:
In a correlational research study or design the researcher seeks to understand what type of relationships between the two test variables have with one another. It tries to identify how the two or more variables are related with each and if they are related in which sense they are related.
According to the given situation, the Dr. Low is using a correlational design. In this he is using two variables namely the mood and willingness to help. He is trying to find the relationship between these two variables.