Biostatistics & Research · patient case question
Which study design provides the LEAST reliable evidence?
Patient case: Evidence, and a Patient Irradiated Ten Years Ago
Patient: 66-year-old male
Chief Complaint: Two non-restorable mandibular molars requiring extraction.
Background: Squamous cell carcinoma of the floor of mouth treated ten years ago with surgery and RADIOTHERAPY to the head and neck, total dose approximately 66 Gy. Currently disease-free. His new dentist is reviewing the published evidence on managing extractions in irradiated bone.
Medications: None
Vital Signs: BP 132/80 mmHg · HR 74 bpm · RR 16 · T 98.4°F
Findings: Teeth #30 and #31 are non-restorable with periapical radiolucencies. Overlying mucosa is intact. Xerostomia with rampant cervical caries on the remaining dentition. Trismus with maximum opening 32 mm.
Show answer and explanation
Correct answer: C. Case-control study
- A. A systematic review with meta-analysis sits at the TOP of the evidence hierarchy — a comprehensive, pre-specified synthesis of all eligible studies.
- B. The RCT is the strongest primary design. Randomization distributes confounders, known and unknown, between groups.
- C. CORRECT of the designs listed. A CASE-CONTROL study is RETROSPECTIVE and observational: it identifies people who already have the outcome, matches them with controls, and looks backwards for exposure. It is therefore highly vulnerable to RECALL BIAS and SELECTION BIAS, cannot establish temporal sequence with confidence, and yields an odds ratio rather than a true risk. It is efficient for rare diseases and long latency periods, but it sits low in the hierarchy.
- D. A prospective cohort follows exposed and unexposed groups FORWARD to the outcome. It establishes temporality and calculates true relative risk, making it stronger than case-control.
Note: The hierarchy, top to bottom: systematic review and meta-analysis > randomized controlled trial > cohort > case-control > case series and case reports > expert opinion. Note that CASE REPORTS and EXPERT OPINION are weaker still than case-control — if they appear as options, they take the bottom place.
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