21.   But more research is needed if such chemical attractants are to become a viable means of control.

22.   But those applications need further research, Krauss said.

23.   But they also said further research was needed into the effect of repeated ear lobe punctures on patients who require frequent glucose screening.

24.   But, he added, further research is needed.

25.   But, noting the small size of the study, he cautioned that more research was needed.

26.   Experts agree that more research is needed.

27.   EU advisers believe more research is needed.

28.   Further research is needed.

29.   Further research is needed before those links can be confirmed, according to the report.

30.   Further research is needed, but what little evidence we have shows no such positive impact from test scores or passive civic knowledge.