You’ve heard it a thousand times that “passive voice” is bad and “active voice” is good.
In general, I also agree with that advice.
For example, “I wrote this e-mail” (active voice) is a much better way of stating the fact than “this e-mail was written by me”.
However, as with everything else under the sun, there are exceptions to this rule as well.
Sometimes passive voice is better because it does not always make sense to identify the agent of an action.
For example, consider the sentence “The patient was transferred to the surgical service,” provided as an example by Lester S. King, M.D., the esteemed former Senior Editor of the Journal of the American Medical Association (JAMA), in his great book Why Not Say It Clearly: A Guide to Scientific Writing (Little, Brown and Company, 1978).
“Does it really matter for us to know who exactly transferred the patient to the surgical service?” King asks.
Of course not because what we are really interested in is the kind of treatment the patient receives.
Here is the “Lester Rule”: if the identity of an agent is not crucial to the meaning of a statement, then it is permissible to use passive voice construction (like I just did).