Statistical Analysis and Sample Size
The sample size calculation was performed in relation to the difference
in the postoperative decrease in
Hb level among the 3 groups using G*Power Version 3.1.7 (Franz Faul;
UniKiel, Germany) software. On the basis of our preliminary data of 60
patients who underwent primary total knee arthroplasty and were assessed
for the same measure, the mean
decrease in Hb level (and standard
deviation) was 39.3 ± 5.89 g/dL. A reduction of 10% (4 g/dL) in Hb
level in patients who received a daily dose of 10,000 IU from
preoperative day 5 to postoperative day 3 was recorded as a significant
difference. In summary, 60 patients per arm were needed, with a power of
0.90 and a significance level of 0.05.
We compared the quantitative data between groups using 1-way analysis of
variance and Tukey’s post hoc test. The Pearson chi-square test or
Fisher’s exact test was used to analyse qualitative comparative
parameters. All analyses were performed using SPSS for Windows, Version
19.0 (SPSS Inc, Chicago, IL). Significance was set at P <
0.05.