Graphical Analysis

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Information about Graphical Analysis
Business-Finance

Published on October 30, 2008

Author: drrchrds

Source: authorstream.com

Slide 1: Lean 6 Solutions Better Quality, Faster Slide 2: Graphical Analysis Techniques Run Charts : Run Charts What is a Run Chart? : What is a Run Chart? A graph of data points plotted in chronological order. A common tool to display how a process performs over time. Run Chart Features : Run Chart Features 140 Vertical axis shows the numerical value or count Data points plotted in time order Points are connected by a line to aid in visual interpretation Horizontal axis indicates time When use a Run Chart : When use a Run Chart In the measure phase, to measure current process performance against target values and to determine the baseline for your current process. In the analyze phase, to analyze data for variation and patterns that can not be seen in tables or spreadsheets. In the improve phase to evaluate progress after process changes or improvements. Run Chart Data : Run Chart Data Data must be collected regularly from a process. Examples include: Monthly calculations of cycle time Hourly measurements of customer queue time. Weekly yields from the past two years Slide 8: Analyzing run charts Extreme value differences between points indicate excess variation, which will cause points to be outside targets. Analyze the chart for process variation. Too much variation can keep you from meeting your targets. Maximum Variation Outside target Slide 9: Analyzing run charts Process Shift A process shift will generally occur quickly and as a result of a dramatic change in the process. Analyze the chart for process shifts. This occurs when the average of the process has increased or decreased. Slide 10: Analyzing run charts Clusters A process shift will generally occur rather quickly and as a result of a dramatic change in the process. Analyze the chart for clusters. This occurs when there is a shift in the process average, a trend, or a cyclical pattern. Slide 11: Analyzing run charts Analyze the chart for process drifts. This occurs when 6 or more points in a row are decreasing or increasing A process drift is a series of small changes that occur to processes over time. Process Drift Constructing Run Charts : Constructing Run Charts Step #1: Enter Data labels and data in spreadsheet as shown on the right. Multiple run charts can be made on one graph. Step #2: SPC XL > Quality Tools > Run Chart. Step #3: Enter the data range and X axis labels as shown below. Constructing Run Charts : Constructing Run Charts Step 4: SPC XL will create a run chart like the one on the right. Step #5: Further customization of the run charts can be done by clicking on the desired area of the chart you want to change and giving the desired inputs in the appropriate dialogue boxes. Keys to Success : Keys to Success Use run charts to analyze process variation over time. Analyze the process for shifts, drifts, excess variation or clusters. Ensure that your data is collected and recorded in time order. Collect enough data to see if variation is occurring. 24 data points is a recommended for a reliable interpretation. Tool: Pareto Charts : Tool: Pareto Charts The Pareto Principle : The Pareto Principle This is also known as the "80/20 Rule". The rule states that about 80% of the situations of the problem can be traced to 20% of possible causes. The Pareto principle was developed by an Italian economist who noticed that 80% of the wealth was owned by 20% of the population. The Pareto Principle : The Pareto Principle The Pareto principle implies that we can frequently solve a problem by identifying and attacking the “vital few” sources. This principle can be applied to most systems and processes. The concept is used to dissect a large problem into smaller pieces and in order to identify the biggest contributors. Pareto Principle Examples : Pareto Principle Examples Most of the equipment breakdowns are due to a small percentage of the equipment. The majority of calls to a IT help desk are attributed to a small number of reasons. Most of the errors in any process occur in one or two process steps. Only a handful of students in the school district account for most of the tardy events. Slide 19: What is a Pareto Chart? A graphical representation of the Pareto Principle. A series of bars whose heights reflect the frequency of the problem. A graph where data is categorized to expose patterns. Pareto Chart Features : Bar height shows relative importance; in descending order Bars represent each stratified category Pareto Chart Features Vertical axis shows relative percentages “Other” category can be used. It’s always last. Vertical axis shows count of data points Red line shows cumulative percentages Slide 21: When use a Pareto Chart? In the measure phase to identify which problem should be studied. In the analyze phase to verify which potential causes of the problem are most significant. In the improve phase to determine if the problem has improved. Analyzing the Pareto Chart : Analyzing the Pareto Chart The Pareto Principle applies if one or more categories account for a large percentage of the occurrences. Look for the bars that are much taller than the rest. If Pareto Principle Applies : If Pareto Principle Applies Focus your improvement efforts on the largest category or categories of the Pareto Chart, in order to achieve the maximum gain. Only focus on a smaller bar if it has a larger impact or is easier to fix. Using only the data from the large categories of the Pareto Chart, determine if they can be further stratified into additional categories. Lower Level Pareto Charts : Lower Level Pareto Charts 2nd level Pareto Chart If the data from the Pareto chart can be stratified further, create 2nd or even 3rd level charts. Analyze these charts to determine if the Pareto Principle applies. When you’ve narrowed down the problems on the deepest levels you will start finding root causes. 1st level Pareto Chart 3rd level Pareto Chart Analyzing the Pareto chart : Analyzing the Pareto chart The Pareto Principle does not apply if all the categories account for an approximately equal percentage of the occurrences. All the bars are about the same height. If Pareto Principle doesn’t apply. : If Pareto Principle doesn’t apply. Do not analyze the tallest bar any further. It is clear that this categorization is not related to the root cause of the problem. You need to find another way to look at the data. - Determine if there is another way to stratify the data. - Normalize the data (make all the categories comparable by making the thing you are measuring into a rate). The Other Category : The Other Category Occurrences in the “other” category should be redistributed to existing categories or a new category should be created If you create an “other” category ensure that it is not one of the larger bars on the chart. Collecting the Data : Collecting the Data Data has to be collected in categories. The categories should be determined before the data is collected. A sample size of 50 data points is recommended. If 50 data points are not available, obtain as many as possible. The data only represents a snapshot of the process at a period in time. Since processes change over time, the data needs to represent the process you are analyzing. Constructing Pareto Charts : Step # 1: Stratify the data you are going to collect into logical categories. This can often be done as a team brainstorming activity. Step #2: Enter Pareto labels and data into excel spreadsheet. Step #3: SPC XL > Analysis Diagrams > Pareto Chart Highlight the data in the spreadsheet to be included in the Pareto Chart Constructing Pareto Charts Constructing Pareto Charts : Constructing Pareto Charts Step # 4: Determine the look of the Pareto chart by selecting your settings. The ” # Groups” setting will determine the number of bars in your chart. If you choose a smaller number of groups than you have categories, SPC XL will create an “other” group. Constructing Pareto Charts : Step #5: SPC XL will create a Pareto chart in the “Pareto Chart” tab. Step #6: SPC XL will create a report of the count and % total by category in the “Pareto Report” tab. Constructing Pareto Charts Constructing Pareto Charts : Step #7: Double clicking on the bars of the pareto chart will allow bar color editing, adding of values for the lines, font size changes and other desired customization of the chart. Constructing Pareto Charts Keys to Success : Keys to Success Apply the Pareto principle early in your process improvement efforts to identify the vital few causes. The Pareto principle applies if a small number of causes account for a large portion of the problem. The data needs to be representative of the period in time that you are analyzing. If the Pareto principle applies, see if you can further stratify the data into other categories. If the Pareto principle does not apply, look for other ways to stratify the data.

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