Final answer:
The researcher is using a dependent samples t-test to compare depression scores before and after treatment in one group of clients.
Step-by-step explanation:
The researcher comparing depression scores before and after treatment in one group of clients is using a dependent samples t-test.
A dependent samples t-test, also known as a paired samples t-test, is used to determine if the mean scores of two related groups are significantly different from each other. In this case, the researcher is comparing the depression scores before and after treatment, which are related measurements from the same group of clients.
For example, if the researcher measured the depression scores of the same group of clients before and after a treatment intervention, they can use a dependent samples t-test to analyze the data and determine if the treatment had a significant effect on reducing depression.