The nurses are aware that the vest wearing policy is introduced to reduce medication errors. Wouldn't the nurses just be extra cautious while wearing these vests (not because there are fewer distractions around them but because they know they are been observed)?
Also : Who cares if the true reason is less interruptions? The environment is reducing the error rate.
One day, will someone notice that the vests have no obvious link to the tasks and promote removing hem for cost cutting?
All I'm saying is the nurse example doesn't really prove the main argument, which is that fewer interruptions equals fewer errors. Right now, it appears everyone reading this wants to apply this seemingly proven technique in their own work place, when (maybe) all they need is a device that reminds them that 1.) they make mistakes and 2.) their mistakes are being measured and observed.