You must never begin an experiment if you do not know, in advance, how you will analyse the data.
Experiments are fundamental to the progress of science.
They are the means by which theories are developed, tested or refuted. In these notes experiments are restricted to those that require some statistical consideration of the data. Experiments need to be designed, in the sense that they do not just happen'. It is obvious that experiments do not happen by a process of divine creation, but many are undertaken without a formal design. Failure to design experiments almost always leads to a waste of time and resources.