1.   A number of methodological criticisms have been made of these studies which cast serious doubt on the validity of their findings.

2.   Even among some Taft supporters, however, there were serious doubts that the controversial senator could win the presidency.

3.   For these reasons, the Conservatives are a little more responsive to widespread expressions of serious doubt on their own backbenches.

4.   Some government ministers had serious doubts as to whether the policy would work.

5.   They have some serious doubts as to his honesty.

6.   Although I soon convinced him of my innocence, I think he still has serious doubts about my sanity.