If there are no results, then further research or another date range is needed.
I'm looking at the independent clause ("then further research or another date range is needed").
Problem #1 is that this is in passive voice. However, for the sake of argument, let's say I want to leave it that way. The actor(s) of "is needed" have been clipped, which is fine in passive voice.
However, if I were to revise the sentence to make it active, it would look something like this:
If there are no results, then you will need to do further research or enter another date range.
There really isn't a way to add in an actor, make the verb active, and leave the sentence intact.
Which makes me suspect that there's something wrong with the passive itself.
Hm. What do you think?