Spine
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A retrospective cohort study. ⋯ 3.
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Retrospective cohort study of the prospective collected American College of Surgeons National Surgical Quality Improvement Program database. ⋯ 3.
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Retrospective review of a prospective cohort. ⋯ 3.
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Retrospective review of an administrative database. ⋯ 3.
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Retrospective case-control study. ⋯ 4.