A hospital administrator states: 'We recently installed hand sanitiser dispensers at the entrance of every ward. Over the following three months, we observed a 20% reduction in the rate of hospital-acquired infections compared to the three months prior. Therefore, the new dispensers are the cause of this improved patient safety.' Which of the following, if true, would most weaken this argument?
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A
The hospital also implemented a mandatory staff hand-washing training program at the same time the dispensers were installed.
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B
The cost of the hand sanitiser was higher than the cost of the infections it was intended to prevent.
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C
A patient satisfaction survey conducted during the same period showed a slight increase in overall patient happiness.
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D
The previous three-month period had an unusually high rate of infections due to a rare viral outbreak.