Table 5.

Meta-regression coefficients and model diagnostics

Covariate	β (Estimate)	95% CI	t-value	p-value	Interpretation
Study Era (per decade)	−0.127	−0.198 to − 0.056	−4.12	0.001	Significant mortality reduction
Mean Follow-up Duration	−0.089	−0.142 to − 0.036	−3.74	0.003	Longer follow-up reduces mortality
Mean Age (years)	−0.028	−0.051 to − 0.005	−2.89	0.019	Older cohorts show lower log(SMR)
Severe TBI (%)	+ 0.021	0.006 to 0.036	3.21	0.007	Higher severity increases log(SMR)
Log₁₀ Sample Size	−0.034	−0.067 to − 0.001	−2.41	0.045	Larger studies report lower risk
Residual Heterogeneity τ²	0.018	—	—	—	Substantially reduced