The quality of information provided by sales representatives to physicians also has been investigated in a few studies. Similar to advertisements in medical journals, researchers have noted the low quality of information provided by detailers to doctors. Studies in a few countries have revealed that detailers regularly omitted medically necessary information and made inaccurate claim to promote positive value of a product without supported by research evidence. No published study is available to evaluate the content of detailers’ presentation to doctors in X. No recent data in Y is available since the only study in 1998, conducted to answer this question.
Looks pretty good. One or two things need changing though...
1. ...physicians also has been investigated...
In English we generally swap the 'also' and 'has' around, so that it reads '...physicians has also been investigated...'
2. ...inaccurate claim...
I think there should be an 's' on the end of 'claim', to make 'claims'.
3. ...to promote positive value of a product without supported by research evidence.
I think it should be 'to promote the positive value (or values) of a product without the support of research evidence' or '... of a product without being supported by research evidence' or ...'without having the support of research evidence'.
Sorry, there are so many possibilities for that one!
4. ...content of detailers’ presentation
This makes it sound like there was only ever one presentation. I guess there was more than one because you have used the apostrophe after the 's' on detailers. In which case you should say 'detailers' presentations'? If there WAS only one presentation, it is more likely that you would use 'the' in front of detailer's and put the apostrophe between the r and s.
5. The last sentence is tricky. I think you meant to say, 'No recent data about Y is available, since the only study conducted to answer this question was conducted in 1998.'