The term "parameter invention" refers to inventions that are defined by establishment of new parameters that have not been known beforehand. As for a "selection invention" the difference to the prior art can be known quite easily, on the other hand as for parameter inventions, since the parameter has not been know beforehand, it is not obvious that the invention posses novelty compared to the prior art and therefore mostly it is necessary to reproduce and analyze the prior art in order to understand the difference.
For parameter inventions it is especially important to consider the requirements for the specifications (especially concise expressions), novelty and inventive step. As for the former they have to be clear enough in order to enable someone skilled in the art to work the invention without difficulty. As for the later, no matter how new the parameter may be in general patentability is not recognized for parameters that define properties or characteristics of former subject material.