- The sample size was calculated by using the averaged of pain level at rest after treatment from the single thoracic manipulation combined with special massage group and single thoracic manipulation group, after the preliminary procedure that will be conducted with ten subjects per each group. After that, the variance was calculated by using the equation σ2 = (n1-1)s12 + (n2-1)s22/(n1+n2)-2 and the result will be used for calculate the sample size. A drop out rate will be set as 20%. The effect size (∆), the significant level of lower than 0.05 (Zα(0.05) = 1.96) and a power of test at 90 percent (Zβ(0.2)=1.28) was used to calculate in the equation as follow: n/group = "2(Zα + Zβ)2σ2" /"∆2"