The Chan et all retrospective study of vacuum versus forceps is really a study of difference of practice and not a study of different instruments.
Rae
P B
PB
D005113:Extraction, Obstetrical / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D009772:Obstetrical Forceps; D018579:Patient Selection; D010818:Practice Patterns, Physicians'; D011247:Pregnancy; D012107:Research Design; D012189:Retrospective Studies; D012307:Risk Factors; D014620:Vacuum Extraction, Obstetrical / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*