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Industrial Statistics with Minitab by Xavier Tort-Martorell Llabres, Lluis Marco Almagro, Pere Grima Cintas

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4.5 Scatterplots with Panels

Consider the data in file REHEAT.MTW, included in the Minitab sample data folder, to illustrate how to construct scatterplots stratified by a third variable called a panel variable.
The data contained in this file is collected from an experiment carried out in a company specializing in frozen foods. The purpose is to determine the oven temperature and the cooking time of a frozen meal so that its flavour is the best. To achieve this, different temperature and time values are used and each sample meal is tasted by three judges who assign a quality score on a scale of 0 (worst) to 10 (best). The file is organized as follows:
Column Variable Label
C1 Operator Oven operator
C2 Temp Oven temperature
C3 Time Cooking time
C4 Quality Average tasting score, going from 0 to 10

Graph > Scatterplot >

nc04uf015.eps
nc04uf016.eps

This plot shows a scatterplot of the Quality variable in relation to the time variable, for each temperature value used in the experiment. Observe that for low oven temperature values (the three scatterplots above) the best quality measures are obtained at very high values of time. On the contrary, with higher temperature values (bottom plots) ...

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