Final answer:
The null hypothesis for a dependent-samples t-test is μD = 0 because it assumes no difference between the paired variables.
Step-by-step explanation:
In a dependent-samples t-test, also known as a paired t-test, we compare the means of two variables that come from the same individuals or subjects. The null hypothesis, denoted as μD = 0, states that there is no difference between the two variables. In other words, it assumes that the mean difference between the paired observations is zero.
This null hypothesis is set because we want to test whether there is a significant difference between the variables. If the null hypothesis is rejected, it implies that there is evidence of a significant difference, and we can conclude that the two variables are not equal.