2.3. Statistical analyses
The 2003 and 2007 mortality rates by age group were initially
compared by the Friedman test for multiple subpopulations. The
Wilcoxon signed ranks test was used to compare the mortality of
two related subpopulations.
The positivity of the blood culture examinations among tested
specimens from patients with suspected sepsis was estimated by
meta-analysis to combine eligible studies. Likewise, the proportions
of Gram (+) bacteria, Gram () bacteria, and fungus among all
identified microorganisms from positive blood culture were
estimated by meta-analysis using the same approach. All
meta-analyses were performed using a random effect model.
Subgroup analysis was performed among different regions of
China, as well as among different time periods. Additional
subgroup analysis was performed among neonatal or pediatric
patients. The relative ratios (RRs) and 95% confidence intervals
(CIs) of the synthesized positivity of blood cultures or proportion
of microorganisms between different subgroups were calculated
based on the estimated percentage and the sample size of each
subgroup.
Nonparametric tests were conducted with SPSS 13.0 software
(Chicago, U.S.). The meta-analyses were conducted with the
statistical software Comprehensive Meta-Analysis 2.0 (Biostat,
Englewood NJ, USA). RR and 95% CI was calculated using Microsoft
Excel 2010, with the formulas for 95% CI of RR = exp(ln(p1/
p2) 1.96 * sqrt(1 / (p1 * N1) + 1 / (p2 * N2) – 1 / N1 – 1 / N2)), and p
value = 2 * (1 – normsdist(abs(p1 – p2) / sqrt(p1 * (1 – p1) / N1 + p2 *
(1 – p2) / N2))). All statistical tests were two sided using an a level of
0.05.