In this linear model the fs are constant linear coefficients of the indupendent variables X, that indicate the conditional effect of each independent variable on the determination of the dependent variable, Y. in the population. Thus, the coef ficients are parameters in the linear regression model. A series of production runs would then be made to obtain measurements of various combinations of in dependent and dependent variables. (See the discussion of experimental design in Section 13.2.) u14 Example 12.2 Store Location (Model Specification) The director of planning for a large mailer was distinted with the company's new store development experience in the past 4 years 25% of new stores failed to obtain their projected sales within the 2 year trial period and were closed, with substantial economic losses. The director wanted to develop better criteria for choosing store loca tions and decided that the historical experience of successful and unticcesul stores should be studied