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Unformatted text preview: 85 Addition to Chapter 4: Independent and Identically Distributed Data for Ordered Data Sets Before we head into inferential statistics, wed like to consider data sets in which the order in which the data was collected matters; e.g., the fill weight of jars of peanut butter on an assembly line. Example. Amount of peanut butter in randomly selected jar (per hour). From Section 4.2, we said that our sampling methods must product independent and identically distributed (IID) data; i.e., a random sample of the population. How do we check if ordered data is IID? Note: If our ordered data is NOT IID (just as if our sample data is not IID and does not model our population), we have no business trying to use statistical methods to analyze it until it is under statistical control. How do we check the IID assumption for time-oriented data? We are going to look at time series plots of the data plots that show the progression of the data over time. From these graphs, we are able to tell if we have identically distributed data by the pattern of the data over time. Also, these graphs suggest there is dependence in the data when consecutive data points give information about each other; e.g., point x negative means that point x + 1 will be positive, and vice versa. So, if order of data collection matters for your data set, well use time series plots to check the independent and identically distributed conditions. First, lets install the Minitab macros that we will use to make time series and random order plots of the data. 86 Minitab Macro Installation Install the macros tsplot.mac and randplot.mac How to install macros? Go to ANGEL: Lessons -> Minitab macros; install both tsplot and randplot 1. Left-click on the macro, e.g., tsplot.mac 2. Mouse over the link for the macro to stop it from automatically downloading 3. Right-click on the macro; e.g., tsplot.mac 4. Left-click on Save Target As 5. For Save as type , select All files 6. Save the file as: C:\Program Files\MINITAB 15\English\Macros\tsplot.mac 7. Verify that Windows has NOT appended .txt to the above file....
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