Spine
-
A systematic review. ⋯ 3.
-
Retrospective analysis of prospectively collected data. ⋯ 3.
-
Prospective observational cohort study. ⋯ 4.
-
A cross-sectional survey with a longitudinal follow-up. ⋯ 2.
-
Secondary analysis of data from a concurrent randomized trial and cohort study. ⋯ 2.