Graphical Methods

Question 1

Scatter Diagram

Answer 1

• Provides relationship between two variables, and provides a visual correlation coefficient.

Question 2

Why would you guys Scatter Analysis and Scatter Plots?

Answer 2

Scatter Analysis is used when you need to compare two data sets against each other to see if there is a relationship.

Scatter Plots are a way of visualizing the relationship; by plotting the data points you get a scattering of points on a graph.

Scatter Diagrams are used to show the “cause and effect” relationship between two kinds of data, and to provide more useful information about a production process

The analysis comes in when trying to discern what kind of pattern, if any, is present, and what that pattern means.

It is this kind of analysis we are talking about when we are tying to get at the roof cause of an issue.

Question 3

Specific instances of when to utilize Scatter Diagrams

Answer 3

• Paris of numerical figures are present
• Dependent variables have multiple value for each figure associated with the independent variable
• Defining if there is a relationship between two variables

Question 4

What kind of data should you use on Scatter Analysis?

Answer 4

• Continuous Data
  
  • Lets you measure things deeply on an infinite set

Question 5

Scatter Plots and Correlation

Answer 5

• Scatter Plots only show correlation. They do not prove causation.
• The example often used is shark attacks and ice cream sales. There may be a correlation between the two, but ice cream does not cause shark attacks — the heat of the day does. In other words, more people are in the water on hot days equaling more shark attacks, and more people buy ice cream on hot days

Question 6

Histogram

Answer 6

• Bar chart showing the frequency of an outcome
• Use to visualize what’s going on
• Can reflect the voice of the process
• Useful in evaluating the shape of the data

Some questions we can to evaluate when interpreting a histogram:

• How many peaks are there?
• Are there outliers?
• Does it look approximately symmetrical and bell-shaped?
  
  • If not, the process being reflected is not a normal distribution

Question 7

Bell-Shaped Histogram

Answer 7

• If there is a bell shape, your data is normally distributed and hence, no variation (or influence from other factors like the 6Ms)
  
  • Method
  • Mother Nature
  • Man/People
  • Measurement
  • Machines
  • Materials

Question 8

Spike Histogram

Answer 8

• If there are multiple spikes in the chart, there is likely variation in the process
  
  • Variation=lack of consistency

Question 9

Even Histogram

Answer 9

• If all of the bars are at the same level it’s not likely that we are measuring the process in the correct manner

Doing statistical analysis usually involves the following:

1. Measuring the central tendency
   
   1. Mean, Median, Mode
2. Measure of the variation
   
   1. Inconsistency

Question 10

Create a Histogram

Answer 10

1. Get Data
   
   1. Use continuous data from a frequency distribution check sheet
2. Order it and assign categories
3. Create a Bar Chart preserving counts and categories

Question 11

Steam and Left Plot

Answer 11

• Also known as Steam Plots
• Technique to categorize either continuous or discrete values.
• Used to organize data as they are collected
• Methods for showing frequency with which certain classes of values occur.
• Organize data visually and will be able to interpret data and draw conclusions using the plot
• Offers a quick way for simultaneously sorting and displaying data sets where each number in the data set is divided into two parts:
  
  1. Stem
     
     1. All numbers except the last digit
  2. Leaf
     
     1. Only the last digit

Example: The numbers 38 and 52, the steams are 3 and 5, while the leaves are 8 and 2.

Question 12

Uses of a Stem and Leaf Plot

Answer 12

• Effective way to organize the data. A steam and left plot looks something like a bar graph
• Shows data in an organized way, so it can be analyzed easily
• Organizes data so it is easy to compute the median, mode, and quartiles
• Easy to compare different sets of data together at the same time.

Question 13

Fishbone Diagram

aka

Cause and Effect Diagram

aka

Ishikawa Diagram

Answer 13

• Pictorial diagram showing possible causes (process inputs) for a given effect (process outputs)
  
  • In other words, it is a visual representation used to find the cause(s) of a specific problem
• Commonly used in brainstorming and the “open” phase of the root cause analysis

Question 14

When and Why to use the Cause and Effect Diagram

Answer 14

• When
  
  • The problem has multiple probable causes
  • To identify the possible root causes for an effect
  • Identify and sort interaction among the factors on an effect
  • To initiate appropriate corrective actions for existing problems
• Why
  
  • It is a basic step to study a problem/issue to determine the root cause
  • To study all the probable causes of why a process is beginning to have a problem or breakdowns
  • Need to identify areas for data collection for further study

Question 15

How to develop a Cause and Effect Diagram

Answer 15

1. Identify the problem
2. Determine the effect or problem
3. Identify major causes contributing to the effect or problem
   
   1. Man/People
   2. Methods
   3. Machines
   4. Materials
   5. Measurements
   6. Environment
4. Identify sub causes
5. Analyze the diagram

Question 16

Normal Probability Plot

Answer 16

• Graphical technique for normality testing: assessing whether or not a data set is approximately normally distributed.
• In other words, a normal probability plot is a graphical technique to identify substantive departures from normality.
• The normal probability plot is one type of quantile-quantile (Q-Q) plot.
• Compares the values in a data set (on the vertical axis) with their associated quantile values derived from a standardized normal distribution (on the horizontal axis).
  
  • In other words, it plots graph z-scores against the data