Please help me with this sentence. I don’t know it should be ‘have changed’ or ‘have been changed’
Theories about the causes of bird flu [color=red]have changed/ have been changed in the light of recent research.
Both are correct usage 
Peter Kua
Thanks a lot for ur feedback but what you think is the better?
Can you give me a example showing that both are correct usage?
My flight to Australia has changed from Monday to Wednesday.
My flight to Australia has been changed from Monday to Wednesday.
The above sentences have the same meaning.
“Have changed” simply implies that they changed (intransitive verb), with no reference to the cause of this change; “have been changed” implies that someone or something changed them (transitive verb). In this example, both are possible: “theories have changed” simply means that the theories are different from before; “theories have been changed” implies that someone or something undertook to change them according to a certain purpose.
To me it sounds more idiomatic to assume that theories change by themselves; when you have a theory about something and you receive new information on it, the theory in your mind changes by itself, you do not actually “do” the change - it is an inevitable process. Flights, on the other hand, can go with either voice.