A reseаrcher cоnducts аn RCT cоmpаring a manual therapy grоup to a sham treatment group for the outcome of pain intensity (NRS, 0–10) in patients with chronic neck pain. A total of 90 patients are randomly assigned to either the manual therapy group (n=45) or the sham group (n=45). Pain intensity is measured in both groups at baseline and again after 6 weeks of treatment. The researcher wants to compare pain scores between the two groups at the 6-week follow-up. Which t-test should the researcher use to compare pain intensity between the manual therapy group and the sham group at 6 weeks, and why?