An Example of Regression Analysis on Existing Data

Although our purpose in introducing the subject of data treatment has been to provide insight into the design of experiments, the technique of least squares (regression analysis) is often used to fit models to data that have been acquired by observation rather than by experiment. In this chapter we discuss an example of regression analysis applied to observational data. 

The student collected one data pair for each business day for the past nine-months. Each data pair consisted of (1) the amount of money issued by her department in computer-generated checks on that day, and (2) the amount of money in checks that cleared the banks on that day. Table 10.1 is a four-column list of the 177 pairs of data she collected. Each entry gives (1) the sequence, or acquisition number ( Seq ), starting with Thursday, August 8, and increasing by one each business day, five business days a week (2) a nominal scale (that can also be used as an ordinal or interval scale) for the day of the week ( D ), where 1 = Monday, 2 = Tuesday, 3 = Wednesday, 4 = Thursday, and 5 = Friday (3) the amount of money issued in checks ( Iss ) and (4) the amount of money in checks that cleared ( Clr ). 

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