Besides the human factor, there are a huge number of variables that affect the outcome of an experiment. All software is not the same process is a variable, gords are variable, context is variable. That is, one set of processes might be more effective for achieving certain goals in a particular context. than another set of processes We have often made the simplifying assumption that all software is the same, i.e., the same models will work independent of the goals, context size, application, etc. But this is no more true than it is for hardware. Building a satellite and a toaster are not the same thing, anymore than developing the micro code for a toaster and the flight dynamic software for the satellite are the same thing.