Statistical analysis
Descriptive analyses were used to summarize the data, frequency
(percentage) was used for qualitative data, and median (range) was used
for quantitative data. A simple regression model was used to analyze the
trends in the number of trials included, with P<0.05
representing a statistically significant difference, and the year of the
trial was defined by the date of the first ethical approval. All
statistical analyses were performed on a personal computer with the
statistical package SPSS for Windows (version 22.0).