Standard: Use the active voice if you are describing the action of a subject that does something to an object from which that object derives existence or meaning. I broke the window; not, the window was broken.
Darmond and Cliffringer estimated that the cougar population had doubled since the state barred hunting with hounds.
Although there are some verbs which we use exclusively in the passive, e.g.., Rob Casad was born in Bremerton, as well as some for which no passive exists, e.g., John clapped his hands, most of the time writers prefer the active voice over the passive to increase the flow of meaning and clarity.
To get started fast, use the active voice.
In documented research writing, avoid the impersonal constructions below:
Some Common Forms
Johnson sang the song/the song was sung.
Johnson was singing the song/the song was being sung.
Johnson is singing the song/the song is being sung.
Johnson will sing the song/the song will be sung.
Johnson may be singing the song/the song may be being sung.
Johnson may have sung the song/the song may have been sung.
Generally the passive voice causes wordiness and a hiccuping rhythm. Notice the example below:
Rising interest in our nation's hydropower potential, following the passage of the Public Regulatory Policies Act in 1978, has resulted in unprecedented concern by natural resource agencies for the potential cumulative impacts that may be associated with multiple hydropower development in specific river basins. Commonly occurring hydropower impacts that may have significance from a cumulative perspective include the loss of aquatic habitat from streamflow modification, the reduction of visual quality, and the disturbance of recreational patterns.
Natural resource agencies are concerned that because of the Public Regulatory Policies Act of 1978, people will build too many dams in specific river basins and thereby modify aquatic habitat, decrease water clarity, and disturb recreation.
a hit ball
a sung song
a decided that
and make that object a subject (adding a to be verb)...you get the passive voice.
Two more examples
In the mid 1970's it was recognized in the scientific community/change to/ the scientific community recognized.
Five forms of CO2 ocean disposal have been researched by the U.S. Department of Energy/change to/The U.S. department of Energy has researched.