Need help with awkward sentence.This feedback is collected by surveying; because of differences in survey instruments, comparative data is not...

It would be a little easier to help with this if we had
more information about what exactly you are saying.  I say this because I believe that
this passage should be split up into multiple sentences with more explanation.  Given
the information here, this is what I would say.

This data
has been collected through surveys.  However, we are not able to present other data that
is directly comparable.  We are unable to do so because the surveys used to collect
other data have not been the same as the one we used.  Therefore, the data are not
comparable to the data we have collected.

I strongly
believe that it is better to give more explanation in more sentences than to try to fit
too much information into one sentence.