The failure rate of a combined oral contraceptive pill (COCP) with 'perfect use' vs 'typical use' reflects which concept?
- A Theoretical efficacy vs in vivo efficacy — both measured by the Pearl Index
- B Phase I failure (ovulation not suppressed) vs Phase II failure (implantation not prevented)
- C Method failure vs user failure — Pearl Index differences between controlled trial and real-world use ✓
- D Intrinsic failure rate vs extrinsic failure rate due to manufacturing defects
Correct answer: C. Method failure vs user failure — Pearl Index differences between controlled trial and real-world use
Explanation
The distinction between 'perfect use' (consistent, correct use every time) and 'typical use' (real-world use with human error like missed pills) failure rates captures Method failure vs User failure. The Pearl Index (pregnancies per 100 women-years) differs between these two scenarios. For COCPs, perfect use failure rate is ~0.3% while typical use is ~9% — a 30-fold difference highlighting user adherence as the dominant factor. Pearl Index = (Number of pregnancies × 1200) / (Total months of exposure).
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.