In the active voice, the subject does the acting; in the passive voice, the subject is acted on. In general, authors should use the active voice, except in instances in which the actor is unknown or the interest focuses on what is acted on (as in the following example of passive voice).
He was shot in the abdomen and within 10 minutes was brought to the emergency department.
If the actor is mentioned in the sentence, the active voice is preferred over the passive voice.
Data were collected from 5000 patients by physicians.
Physicians collected data from 5000 patients.
The definition of bullying used in the survey was taken from previous studies.
The authors used previous definitions of bullying in the survey.