The correct answer is that they 'are not valid'. If the experiment is biased, it entails that it is not objective. For a experiment, and its results, to be valid, it had to be carried out objectively and taking into account all factors.
It is possible that the results disprove a hypothesis, but to be certain it is necessary to see which was the original objective of the study, as it might also prove to some extent a hypothesis, which is probably also biased.
