State which estimation formula should be computed for each of the following hypotheses concerning a population with an unknown variance:
(a) A neuroscientist measures the mean difference in symptoms of depression before and after a drug treatment.
(b) A forensic psychologist has jurors read a vignette about an alleged crime committed by either a Black or a White defendant. Participants in each group rate the culpability of the defendant.
(c) A cognitive psychologist places a group of participants in front of a computer and asks them to press a key 90 seconds following a prompt to begin timing. She tests how closely (in seconds) their key presses are to the 90-second interval.