In science, a variable is something that can be changed, measured or controlled in an experiment. Scientists look at variables to understand how they affect things. A variable is any one of the things ...

When conducting surveys, two kinds of nonresponse may cause incomplete data files: unit nonresponse (complete nonresponse) and item nonresponse (partial nonresponse). The selectivity of the unit ...

In robust design studies, the important noise factors are varied systematically in off-line experiments and their interactions with control factors are investigated. The choice of the noise variable ...