OCR GCSE Biology A · J247
Specification B3.2e · Paper 1 (Foundation), Paper 3 (Higher)
Revise: ContraceptionNatural family planning has a typical-use effectiveness of 76%; its estimated perfect-use effectiveness is 91–99%. For diaphragms and caps, the NHS gives an estimated perfect-use range of 92–96%, but lists typical-use effectiveness as unknown. “Unknown” should not be treated as 0% or 100%: it means that the table does not provide a reliable figure.