1.   A number of reasons have been put forward to explain these negative results.

2.   Among numerous negative results he found some quite simple compounds, aldehydes and fatty acids, which stimulated oxygen uptake.

3.   Comparison with and without adjustment for smoking gave similarly negative results.

4.   Gram staining and culture gave negative results.

5.   So no real number, positive or negative, squares to produce a negative result.

6.   The investigation, he concluded without surprise, yielded negative results.

7.   A person can be recently infected by HIV and have a negative result.

8.   Drake examined two nearby stars for a few weeks with negative results.