Table 4 Studies with unacceptable high risk of confounding bias
Author, year, country | Study design | Study population | Intervention | Control | Outcome | Comment |
|---|---|---|---|---|---|---|
Bain, 1996, Scotland [15] | Prospective longitudinal study | Patients receiving dental implants | Smoking cessation | No smoking or smoking | Implant failure | Not handling confounding factors |
Mundt et al, 2006, Germany [17] | Retrospective cohort study | Patients receiving dental implants | Former smoker | Current smoker | Implant failure | Not handling confounding factors, in relation to our research question |
Levin et al, 2004, Israel [16] | Retrospective cohort study | Patients receiving onlay bone grafts or sinus lifts | Former smoker | No-smoking | Complications after surgery | Not handling confounding factors |