The passive voice is used extensively in professional writing, making up 25% of all verb uses in published text (approximately 18,500 occurrences per million words). In spoken English, by way of contrast, its use is limited to 2% of all verbs.
The results of the survey were based on qualitative interviews conducted extensively over a six-month period.
The primary use of the passive voice in professional writing can be linked to the removal of the author (“a variation of 0.02% was measured” versus “we measured 0.02 %”) which underlines the scientific objectivity of such statements. This is in keeping with recent Western scientific tradition, though colloquial style (“With this example, we can see that….”) may be used as suits the style of the author.
For more information and exercises with answers, see the pdf attached below.