Understanding_Variation_Problems

Understanding Variation Problems 1) The data file for this problem contains 82 consecutive values for the amount of deviation (in .000025 inch units) from a specified target value that an industrial machining process at a large manufacturer produced under specified operating conditions. Thus in the data 0 means that the value was right on target and -3 means that the part produced measured .000075 inches below the target value. a) Use Minitab to produce a time series plot of this data. b) Describe the plot. Is this process characterized by only common causes or are there any special causes' Is there anything unusual about this data' 2) The data file for this problem contains the average hourly wage (multiplied by 100) for U. S. workers in the manufacturing industries by month over the period from July 1981 to June 1987. a) Use Minitab to produce a time series plot of this data. Describe the plot, what are the most important features of the plot. b) Use Minitab to construct the month to month differences of the average hourly wage data. (Instructions on how to do this are given below.) Plot the month to month differences of this data. Describe the plot, what are the most important features of this plot' To form the month to month differences go to the “Stat” menu, select the item “Time Series” from the submenu, and select the item “Differences” from the resulting submenu. In the subsequent window type the column that has the manufacturing wages into the box labeled “Series” and type the column you wish to store the month to month differences in the box labeled “Store differences in”. Click OK. 3) The data for this problem are monthly sales of a low cost replacement oil filter made by John Deere. The data covers a 48 month period beginning in July of one year and ending in June four years later. a) Use Minitab to produce a time series plot of this data. Describe the plot. What are the most important features of the plot. b) Use Minitab to produce a scatter plot with the oil filter sales on the vertical axis and the month of the sale on the horizontal axis. Directions about how to do this in Minitab are given below. Describe the plot. Are there features of the data that are more easily recognized from the scatter plot than from the time series plot' To plot a scatter plot of the sales versus the month you first must create a column in Minitab that indicates the month. This column must contain numbers that indicate the month. Let January = 1, February = 2, etc. In the Minitab worksheet the column labeled “Month” contains the numerical values indicating the month. To plot a scatter plot go the “Graph” menu, select the item “Scatterplot”, select “Simple”. In the subsequent window type the column that contains the sales data in the box under “Y variables” and type the column that contains the month data in the box under “X variables”. Click OK. 4) The data for this problem are the air freight shipments (in ton-miles) each month (beginning in January for one year) in the U. S. for 10 years. Use Minitab to produce a time series plot of this data. What are the most important features of this plot'