Active and passive forms of sentence structure can completely alter a reader's understanding of the same message. Active sentences tend to be more forthcoming with their meaning, whereas passive sentences aren’t as straightforward.
A study published on the Science Daily website discusses research carried out at Northumbria University. The research looked at how native speakers interpreted active and passive sentences. Dr Dabrowska’s comments on the results of the study included:
"Our results show that a proportion of people with low educational attainment make errors with understanding the passive.” (Science Daily, 2010)
“If a significant proportion of the population does not understand passive sentences, then notices and other forms of written information may have to be rewritten and literacy strategies changed.” (Science Daily, 2010)
An active voice structure
Active voice clearly shows the subject of any sentence carrying out an action: “She ate the juicy red apple”.
She (the subject) ate (the action) the juicy red apple (the object)
A passive voice structure
Passive voice explains the situation, but from the object's point of view: “The juicy red apple was eaten by her”.
The juicy red apple (the object) was eaten (the action) by her (the subject).
Passive voice & academic writing
Passive voice is a frequently used sentence structure in academic writing, because academic writing doesn't normally include the use of personal pronouns. A sentence such as, "I developed this study to improve life on earth", wouldn't fit well into most academic publications. However, if we rewrote that sentence to read, "the study was developed to improve life on earth", then you'd have a perfectly acceptable sentence.
What does all this mean?
Writers should consider their audience. If you are writing for the general public it might be better to avoid the passive voice. Active voice is less complicated, and it tends to be less wordy, which makes it more concise.
It’s important to note that a passive voice isn’t always bad. Passive forms are good when it’s not clear exactly who did an action; for example, “the wall was vandalised at around 9pm last night.” This sentence could be written as part of a police report about a crime. It tells us what the object was and the action that took place, but it doesn’t tell us the subject (who did the action). This may not be known yet. Passive voice is also an accepted sentence structure in academic writing style.
The use of passive voice can sometimes promote a perception that the writer is hiding something. Passive voice is often wordy and more difficult to understand.
Take note of your audience and write in the style that’s most appropriate for them.