Table 2. Mean Durations of Postoperative Analgesia (Hours) in the Three Groups.

Group	No.	Mean Duration of Analgesia, hr	Standard deviation (SD)	Value of Test	P value
Placebo	65	2.06	0.13	120.5	0.0001
Meperidine	65	9.46	0.6	120.5	0.0001
Fentanyl	65	6.27	0.45	120.5	0.0001