Eligible for inclusion were randomised controlled trials, controlled before and after studies, interrupted time series, case control and cohort studies that compared the impact of transfer status on outcomes in patients with trauma. Transfer status was defined as direct admission to a hospital for definitive care, or admission by transfer from another hospital after stabilisation and/or initial treatment. The outcomes of interest were mortality, hospital or intensive care unit length of stay, complications, time to first hospital or time to definitive care. Studies with more than 80% patients with burns were excluded, as were those where transfer status was not the primary exposure of interest.
Most included studies were conducted in urban or mixed urban/non urban settings. Patients had predominantly moderate to major trauma (according to the Injury Severity Score) such as brain/head injuries, blunt or penetrating trauma, orthopedic or blunt pancreatic injury and other traumas. The primary mortality outcome in most studies was in-hospital mortality.
After initial screening had taken place, two reviewers independently selected studies for inclusion. Disagreements were resolved by consensus between three reviewers.