11.   Adam Zaretsky, a Federal Reserve economist, challenged the economic-impact studies that cities had commissioned to back up claims of new revenue and jobs created.

12.   Both sides lack crucial credible evidence to back their claims, he said.

13.   But advertisers cannot, by picking and choosing among studies, present only those that back their claims.

14.   But experimental evidence backing these claims has been paltry.

15.   But Berezovsky has yet to offer any evidence to back such claims.

16.   But he has long resisted backing his claims with scientifically documented evidence.

17.   But he remains unconvinced that good medical studies back up claims of negative side effects to the vaccines.

18.   Colleagues say he still backs the claims but is bitter over their public denunciation.

19.   Clinton left no doubt that he was willing to back those claims on the stump, if necessary.