“…[6, 8, 9, 11, 12, 14, 16, 17, 18 19, 20, 24]. In eight publications it was suggested that observing hand hygiene in the control group might have caused a Hawthorne effect, reducing the difference between control and test group outcomes [9,10,12,15,16,17,19]. In three publications it was suggested that installing extra hand hygiene dispensers in control wards might have the same effect [11,12,20].…”