Training package designed for a wide range of professionals who need to solve problems in a corporate context. Introduction to statistical concepts that are relevant to analyzing data to find the root cause and develop solutions. Customer-focused content
Corporate Profile 47Billion Information Technology
Structured problem solving - training package
1. R E S P O N S I V E N E S S A N D C O M P E T E N C E I N
H A N D L I N G C U S T O M E R C O M P L A I N T S O R
I N Q U I R I E S
June 2016Craig A Zedwick
Structured Problem Solving
2. 2
Craig A Zedwick June 2016
• Structured
o Methodical
o Consistent
o Competent
• Problem Solving
o Specifically with respect to customer problems
o Often technical problems, but can be expanded to logistics,
service, etc.
• Final Product
o A concise response to a customer concern
o Quick & consistent way to respond to a customer’s problem
What is Structured Problem Solving?
3. 3
Craig A Zedwick June 2016
• Problems create stress, especially if they stem from an important customer
• We often dive into the solution phase without truly understanding the problem’s root cause
• Pressure to respond quickly with a solution can lead to bad decisions that make our business
environment more difficult in the future
• Rushing to conclusion causes us to miss key information and insights
• The final result is often specifically tailored to that problem without addressing broader
issues that caused the problem in the first place
• This training package proposes a methodology to avoid the traps listed above
Why Structured Problem Solving?
?
4. 4
Craig A Zedwick June 2016
High-Level Action Flow
3. Confirm that the
problem is under our
control and that we have
power to fix the issue
4. Clearly define success
criteria with customer and
how we will prove success
The ULTIMATE Goal is to show our customer
that we are a responsive & competent partner,
and that we are committed to finding the
solution(s) if the root cause is related to our
product or service
1. Define the problem
or issue (project scope)
2. Get customer agreement
on the problem statement
and plan to address issue
5. Build initial data package to
show urgency and indicate the
direction of our first-phase
investigation
Problems can arise with internal customers
or external customers.
When we reference customer complaints,
both types of complaints should be kept in
mind
5. 5
Craig A Zedwick June 2016
• What the initial response package should not do:
What We Do When Customers Complain?
• Don’t leave the customer to make their own conclusions:
o The spokesman to the internal or external customer needs to manage their
expectations and get alignment on how the investigation will progress
o Every slide/piece of information should be clear & communicate one message
o Customers are often not experts in our product/service, so are not qualified to properly
interpret our data
• Don’t show data over which we have no control:
o If we determine that such data is the true root cause, then we will need to decide how
to communicate this to the customer
o Be prepared to answer the next round of likely questions
o Publishing data too early often results in customer demands for strict limits around
parameters over which we have limited or no control
• Don’t identify a root cause: It’s too early to do anything but
show initial suspicions and our investigative direction
• Don’t publish all data available: It is our job to investigate,
not to show the customer everything and then wait for them to
give us actions
6. 6
Craig A Zedwick June 2016
The majority of problem investigations struggle to either,
(a) reach a satisfactory conclusion (meet Customer expectations), or
(b) reach agreement with the customer to close the complaint
This is often due to the lack of a clear, well-defined problem
statement that is agreed upon with the customer
This will help define the objectives and know when they have been
achieved - it is OK to close the complaint
Step 1: Define the Problem Statement
Take the time required, from the outset, to suitably define and
align on the Problem Statement
7. 7
Craig A Zedwick June 2016
Dig Deeper:
The complaint receiver should do more
than simply pass along the complaint
as given
Get Customer Buy-In:
Know how we can succeed
Step 1: Define the Problem Statement
8. 8
Craig A Zedwick June 2016
Dig Deeper:
The complaint receiver should
do more than simply pass
along the complaint as given
Get Customer Buy-In:
Know how we can succeed
Step 1: Define the Problem Statement, continued
Get as much information & data as the
customer is willing to share
Examples of important information:
– Failure mode (e.g. change in color, late delivery,
product performance, etc.)
– Description of the actions that the customer has
taken to demonstrate that our product is related
to defect mode
– Description of what containment the customer
put in place and how we can demonstrate
recovery
– Defect onset information – specific date or
product lot is best, but could be group of lots
trending toward failure
– Lot usage history – Customer may use our
product in a different order than we produced it
– Correlation data – for us to find root cause, we
need customer data, whether discrete (good vs.
bad) or continuous (preferred)
9. 9
Craig A Zedwick June 2016
Customer should sign off on problem
statement (as accurate & complete)
– If they don’t agree, then what should be
changed?
– Even if they are not sensitive about sharing
proprietary information, getting the customer
to indicate the ways in which our problem
statement is incorrect is still helpful
Customer should define success criteria
– How do we succeed in closing this complaint?
– How can we prove our case if we truly believe
that our product or service is not the root cause
of the problem?
– If we do believe that there is something about
our product/service that links to the customer’s
issue, then how do we prove or disprove the
hypothesis?
• Correlation data only?
• Customer validation?
• Other?
Step 1: Define the Problem Statement, continued
Dig Deeper:
The complaint receiver should
do more than simply pass
along the complaint as given
Get Customer Buy-In:
Know how we can succeed
10. 10
Craig A Zedwick June 2016
Step 1: Flow of Information
Failure Mode
Details
Complaint
Background
Understand
Our Product’s
Contribution
Understand
Convoluting
Customer
Actions
Failure Onset
& Recovery
Information
Customer
Performance
Data
Adjust for
Customer
Actions
11. 11
Craig A Zedwick June 2016
Step 1: Flow of Information
Failure Mode
Details
Complaint
Background
Understand
Our Product’s
Contribution
Understand
Convoluting
Customer
Actions
Failure Onset
& Recovery
Information
Customer
Performance
Data
Adjust for
Customer
Actions
Mechanistic
Studies and
Links
Understand
Good versus Bad
Lots and Data
Populations
12. 12
Craig A Zedwick June 2016
Step 1: Flow of Information
Failure Mode
Details
Complaint
Background
Understand
Our Product’s
Contribution
Understand
Convoluting
Customer
Actions
Failure Onset
& Recovery
Information
Customer
Performance
Data
Adjust for
Customer
Actions
Mechanistic
Studies and
Links
Understand
Good versus Bad
Lots and Data
Populations
Discrete
Customer Data:
Means Comp.
(t-test or ANOVA)
Continuous
Customer Data:
Correlations
and Transfer
Functions
13. 13
Craig A Zedwick June 2016
Step 1: Flow of Information
Failure Mode
Details
Complaint
Background
Understand
Our Product’s
Contribution
Understand
Convoluting
Customer
Actions
Failure Onset
& Recovery
Information
Customer
Performance
Data
Adjust for
Customer
Actions
Mechanistic
Studies and
Links
Understand
Good versus Bad
Lots and Data
Populations
Discrete
Customer Data:
Means Comp.
(t-test or ANOVA)
Continuous
Customer Data:
Correlations
and Transfer
Functions
Root
Cause
= Event
Root
Cause =
Variable
14. 14
Craig A Zedwick June 2016
Example 1:
Edward Stein, an engineer at Acme Electronics Pittsburgh site, informed
us that Acme has observed a 10 ohm trend up in mean resistance from
June 2015, as measured on their finished capacitor test method, that uses
our barium titanate (item # 150369)
What Do We Want to See in a Problem
Statement?
Where does the
problem exist?
Which of our products/services
are involved?
Who can provide more detail if we need it ?
(who is defining the customer experience?)
What quantifies/defines
the extent of the
problem
15. 15
Craig A Zedwick June 2016
Edward Stein, an engineer at Acme Electronics Pittsburgh site, informed us that
Acme has observed a 10 ohm trend up in mean resistance from June 2015, as
measured on their finished capacitor test method, that uses our barium titanate (item
# 150369)
• The process uses two measurement tools (found to provide a significant
contribution)
• The process has been adjusted/corrected over time.
• Another variable is a known key influence on this process and needs to be
considered
Why is it important to discuss/follow up and refine the statement?
Period of interest
Tool to Tool offset is significant The other variable is significant
What Do We Want to See in a Problem
Statement?
16. 16
Craig A Zedwick June 2016
• Elevated defects in a polishing application
o Average defects given by customer first (left chart), but data didn’t show a clear problem
(points above line are bad and below red line are good)
o By aligning with the customer, we realized that the average number of defects was not
the true concern
o The real problem was the higher frequency of defects per batch of polish (right chart)
o Now had a clear time window to investigate
o Timing clearly pointed to a supplier equipment failure as root cause
Step 2: Align with Customer
17. 17
Craig A Zedwick June 2016
• Divides relevant
information from
distractions and false
signals
• Prevents mixing one
problem with another
and getting confused
• Clarifies the
investigation path
Importance of the Problem Statement
18. 18
Craig A Zedwick June 2016
Step 3: Is It Our Problem?
• Every customer problem is our problem
o But not every customer problem is due to our product or service
o Understanding the difference is critical to delighting our customers
• The problem statement should be our first clue about whether the issue is linked
to our product
o Timing and failure mode need to line up with something in our system, or this
isn’t related to our product
o Example: We supply sandpaper rolls to a commercial wood shop
A failure involving smoothness of wood after sanding is likely related to our product.
A failure mode involving uneven staining after sanding could be our problem or it
could be related to the stain supplier, or some combination.
But a failure related to wood splitting when drilled would have nothing to do with us.
• We want to help our customers identify the root cause and solve it
o This may mean proving that our product is not the root cause so they can
investigate elsewhere
19. 19
Craig A Zedwick June 2016
Step 4: What is Success?
• Just as we aligned with the customer on the problem statement, it is
equally critical to align with the customer on the success criteria
• Some customers are happy if everything returns to normal and they don’t
need to understand why
• Other customers can have their performance returned to normal, but
insist on understanding the root cause to avoid a recurrence
• The type of work done in the investigation depends on what the customer
needs to be happy with our response and our product/service
• If a root cause must be shown, then what level of proof does the customer
require to show that we have found the true root cause?
o Some customers are satisfied with historical data analysis showing a correlation
o Demanding customers may expect us to perform experiments to validate that the root
cause we have identified can be controlled and used to turn the failure mode on and off
20. 20
Craig A Zedwick June 2016
• Definition:
o A presentation that communicates to the customer that we
understand their problem and have already devoted key
resources to solving that problem
Step 5: Build the Initial Response Package
Problem Statement
Timeline & Non-Structured Data
Statistical Data Analysis
Validation Results (if done)
Other Investigation Results
Path Forward
• Timing:
o Within 48 hours of receiving
customer complaint
• A Well-Built Initial
Response Package:
The
Root
Cause
21. 21
Craig A Zedwick June 2016
• A Master Data Spreadsheet is the starting point for the entire
investigation
o Should include all information and data related to the customer complaint
o If the customer buys some type of material or tangible product, then the
spreadsheet will list data according to batch number, lot number, or some
other key identifier
o If the customer buys a service (or is an internal customer of some sort),
then the table will list data according to date, project name,
invoice/incident number, etc.
• Include both data and information
o Data – all numerical parameters
o Information – various forms, such as text comments, color, technician
name, etc.
• Be exhaustive
o At this point, we may have ideas, but don’t know for sure what the problem
is or what is causing it
o Listing every available piece of data and information ensures that we don’t
miss anything
Step 5A: Build Master Data Spreadsheet
22. 22
Craig A Zedwick June 2016
• Trend charts are simply chronological charts of a given variable
o If the master data sheet is created in Excel, then:
Each row is defined in Column A by a lot number, technician, invoice number, etc., as described in
previous slide
Each column represents a different parameter
Highlight Column A as the x-axis label and highlight the column of data to plot in a chart
o Only works with data, not other information types like text
• One method to understand the trend chart is to create “control limits”
o There is an entire discipline called Statistical Process Control (SPC) that merits its own
training package (under development)
Good overview can be found at: http://www.statit.com/services/SPCOverview_mfg.pdf
o Control limits are +/- 3 standard deviations around the mean value and can be calculated in
Excel
Mean formula: “=average(B1:B100)” will return the average or mean of the values found in cells B1 to
B100
Standard Deviation: “=stdev(B1:B100)” will return the standard deviation of the values found in cells B1
to B100
Upper Control Limit is the mean value + 3 times the standard deviation
Lower Control Limit is the mean value - 3 times the standard deviation
Excel allows you to fill formulas from one set of cells to a range of cells, so you can create these
calculations at the bottom of your first column of data and then fill to the right in order to copy these
formulas to every column
o Place lines on each trend chart to represent the Upper & Lower Control Limits
o Any data point outside of these limits is considered abnormal and should be investigated
Step 5B: Build Trend Charts
23. 23
Craig A Zedwick June 2016
• Trends are reviewed by the leader of the complaint resolution team
• Should schedule a meeting with the team to decide immediate actions to build the
initial customer response presentation
• Pointers for the team leader:
o Review data and trend charts before this first meeting
Be ready to discuss every trend that has a point of interest
Summarize your findings to make the review efficient
o Key questions while doing data review:
Are the control limits set properly?
Improper limits might arise if the data set chosen as baseline performance is too small or does not include all sources
of normal variation
Is the data from the problem time period in control and within historical range?
Statistical limits are one indicator, but if the customer has never seen a material with a certain parameter as high as
the recent problem batch, that could also be worth investigating
Are there unexplained data shifts?
Mean shifts or variation shifts?
Do they correspond to the customer performance issue?
o Trend charts cannot show correlations to customer data or performance. They only show
whether the parameter is in statistical control
Trends are time-based and may give insight, but should not be used to show customers since there are
better tools for communication of data
Step 5C: Review Trend Charts
24. 24
Craig A Zedwick June 2016
• Why trend charts should not be included in the initial package
o Trend charts only show whether a parameter is showing random variation
or special-cause variation
Trend charts should be used to identify parameters to be investigated
further
o Other charts are better able to represent our data and our conclusions
o The customer will jump to their own conclusions and then may not listen
to our informed explanation
Especially if good vs. bad points are highlighted
Trend Charts & Customer Communication
Wait!
I see a
trend!!!
25. 25
Craig A Zedwick June 2016
• This chart shows particle size on left axis and batch temperature on right axis
o Interpreted as showing a correlation between blend tank temperature and final product particle size
o Coincidental pattern similarities can trick our minds into assuming a correlation
Correlation is a statistical term with a specific definition and requires a body of comparable data
to calculate
Correlations are sometimes very obvious even on trend charts
More often, trend chart patterns that mimic correlation are only present for a small subset of the
entire data set
Trend Chart Example
Aha! Correlation!
Hmm – Maybe Not…
26. 26
Craig A Zedwick June 2016
• Building a time-line to show when a problem first appears and when/if it is resolved is
a critical part of the problem statement and investigation
• Trend charts show how numerical (or structured) data fits with the time-line and
whether any abnormal data exists
• Non-structured data is information that is non-numerical
o Example: Contaminated lettuce in grocery stores
Structured data might include parameters like storage temperature, days since harvested, etc.
Un-structured data would be things like which farm grew the lettuce, which store sold it, and so
on
• Build inputs table
o This shows the various inputs into the product or service for each line item in the master
spreadsheet
o Switching from one batch of incoming material in your process to a new batch might coincide
with the problem start and give valuable insight
o Showing all inputs like people involved (manufacturing operators, technical service, etc.) can
also point out a systematic, but non-numerical pattern
• Remember: Just because something coincides with the problem onset does not
automatically make it the root cause of your problem
Step 5D: Timelines & Non-Structured Data
Coincidence Root Cause
27. 27
Craig A Zedwick June 2016
• Identify abnormal points or trends in numerical data
• Find patterns in non-structured data that coincide with
customer feedback and the problem time-line
• List these items as high priority for further investigation
Step 5E: Analyze Trend Charts and Non-
Structured Data
Abnormal
Patterns
Things to
Investigate
Work with
Experts to
Explain
Possible
Root
Causes
This critical step should be done ASAP before the first
investigation team meeting
28. 28
Craig A Zedwick June 2016
• Build list of possible root causes
o Problem resolution team (PRT) should perform this activity together
o Goal is to brainstorm ideas, not judge ideas or analyze
List everything you can think of
Use any historical documents like Process/Product FMEA or hazard reviews
Look for every possible way that something could go wrong
Organize ideas into categories as you go along, then re-organize at the end if
needed
o Good tool for this? Fishbone Diagram
Pre-defined categories help organize and give ideas on types of root causes
Build diagram using diagram software like XMind, Visio, etc. (I like XMind)
Step 5F: Root Cause Brainstorming
Try separate meetings for brainstorming ideas and screening
those ideas
29. 29
Craig A Zedwick June 2016
• Common Main
Categories
o Manpower
o Machines
o Methods
o Materials
o Measurements
o Environment
• Problem listed in
circle label at the head
of the fishbone
• May need multiple
diagrams if there are
multiple problems
Fishbone Diagram Example
30. 30
Craig A Zedwick June 2016
• The High Priority list will form your action plan
• Fishbone diagram and idea list should usually be kept as internal documents
o Too much detail and (maybe) proprietary information to share with customers
o Can share action plans built from the idea list
Step 5G: Root Cause Idea Screening
Ideas that:
• Have no data
to check
• Can be
immediately
disproven
• Cannot be
reasonably
investigated
• Most likely
root causes
• Easiest to test
• Fit known
mechanisms
• Can be
controlled
1. Prioritize high
priority ideas
2. Assign
owners to
each action
3. Assign target
completion
dates
31. 31
Craig A Zedwick June 2016
Step 5H: The Investigation
• Review paper batch cards
• Confirm metrology is operating
correctly
• Perform extra testing
• Many others based on idea list
Investigative actions are
coordinated by PRT Lead
– Different ideas require different investigation
activities
– Statistical analyses to find links to
performance data (done by CQE & MQE)
• This can be done for all continuous variables
that CMC collects
• More details in upcoming slides
• Try to correlate to any continuous customer
data
– Validation testing (done by many functions,
depending on nature of test)
• This is used to prove or disprove a hypothesis
• Example hypothesis: The dosing control valve
is not functioning correctly
• Possible validation: Perform dosing test using
bucket to collect and weigh material
Other Possible Actions:
32. 32
Craig A Zedwick June 2016
• Statistical Analysis
1. Compile all data gathered to this point into the master spreadsheet
2. Add customer feedback data column(s) to master spreadsheet
Continuous (i.e. slurry lot-based) data can be input directly
Discrete data should indicate good vs. bad using numbers
Example: 1=good, 5=bad
Tip: Color coding good and bad rows of data may help
3. See next slides for how to analyze based on customer data type
Step 5H: The Investigation
4. Perform correlation and regression
analyses as detailed on the
following slides
NOTE: A correlation alone does not prove
cause-effect relationship and cannot be used to
predict behavior
33. 33
Craig A Zedwick June 2016
• Discrete Data from a customer is usually in the form of good vs. bad
o Either a product works or not
o If a product or service is given a subjective rating (e.g. from 1 to 5), then that can be analyzed as
continuous data or you can combine the best and worst rating numbers to create a good vs. bad set of
data
This is often used in marketing analysis to combine ratings like “satisfied” and “very satisfied” in order to
find patterns
o Numerical data being analyzed can then be associated with the good products or the bad products
o There is a statistical test that can be run to see if the entire set of “good” data is truly different than
the entire set of “bad” data
o This is called a t-test and the output of this test is called a P-value
• See the embedded video for an example of how to use Excel to quickly generate t-test P-
Values for good vs. bad data sets
• Investigate any data columns with a P-Value < 0.05 further
o P-Value indicates the probability of the two populations NOT being different
o So a very low P-Value means that you are confident that these two data populations are actually
different
o Because you have divided one parameter into two data sets to represent good and bad customer
feedback, if they are statistically different, then this parameter should be investigated further
Analyzing Discrete Data
34. 34
Craig A Zedwick June 2016
• Continuous data is something like temperature or a person’s height
o Any data that can be measured directly
o Also includes things like survey or census data given as percentages
o Continuous data can be summarized by taking the average and calculating the standard deviation
• The most common analysis tool for continuous data is a linear correlation
o This determines if two different parameters are related to one another by a straight line relationship
o In Excel, this would be shown using a x-y scatter plot with a linear trendline
o The correlation coefficient is called R and can be either positive or negative
A positive R means that when one variable increases, so does the other (direct correlation)
A negative R means that when one variable increase, the other variable decreases (inverse correlation)
Analyzing Continuous Data
o Excel can easily calculated the R value and the R2 value
The R2 value multiples R by itself to give a value that is always positive
See the embedded video for an example of how to perform this analysis
• Critical Concept 1: Correlation does not mean causation
Just because two variables are linked in some way does not mean that
one variable is causing the other variable
• Critical Concept 2: Correlation does not mean significance
Two variables may have a high R-Value, but if the slope of the line is
flat, then it means that there is no real movement in one variable when
the other changes
35. 35
Craig A Zedwick June 2016
• Correlation or coincidence does not
always mean causation
• Every parameter has error bars around
each value – understand error bars to
avoid wrong conclusions
Cautionary Notes
• Multiple similar signals
correlating to performance
may be confirmation or may
be covariant
• Check your charts! Outliers
can make random data look
like a correlation
36. 36
Craig A Zedwick June 2016
• Background
o Pam and Sue’s is a department store with 250 locations
o Their current method of choosing new locations is by categorizing the stores into one of
seven categories based on a variety of factors
o Their predicted sales for new stores is becoming less and less accurate over the past few
years
o Now want to know if there is a better way to predict the sales for potential store locations
to do a better job of choosing new locations
• Data set
o Variety of demographic data collected by governmental agencies for the area within 15
km of each of the existing stores (continuous data)
o Also lists the Store Type category which is a value from 1-7 (discrete data)
• Can this data set be used to build a predictive model for store sales?
o What demographic data actually correlates to sales?
o Can the correlated parameters be used to build a model?
Working Example
37. 37
Craig A Zedwick June 2016
• The goal of the first 48 hours is to develop an investigation plan
o The investigation plan should list the prioritized actions
o Four possible issues that should lead to further investigation:
1. Abnormalities in the parameter’s trend chart
2. Some Non-Structured Parameter coincides with the defect onset
3. There is a high likelihood parameter identified in the fishbone diagram
4. There is some correlation or mean shift associated with a parameter when compared
to the customer’s performance data
o The more of the above issues are linked to a parameter, the higher its priority should be
The actions associated with investigating each parameter will differ, so a fixed
process cannot be used for the investigation after this point
By using this process in the first 48 hours, we will deliver value to the customer and
provide a good plan for our further investigation to follow
Step 5I: The Investigation Plan
Statistical
Analysis
Investigation
Plan
Root
Cause
Idea List
38. 38
Craig A Zedwick June 2016
• Remember:
o The initial data package is just the first response to the customer
o Future data packages and presentations will vary, depending on the path of the investigation
• Data Package Outline
1. Problem Statement
Should match what was agreed with the customer
Show tables or charts that clearly define the onset and recovery (if there is recovery)
2. Time Line & Non-Structure Data
Clearly highlight onset and recovery points
Avoid too many colors or fonts, except around the onset and recovery points – don’t confuse customer
Don’t show too many data points before the onset point unless there is a specific reason
3. Statistical Analysis Results (selected charts, not full data set)
Include only those parameters that show a reasonable correlation or link to customer performance
Be careful about which parameters are shared to protect any intellectual property
May need to normalize the numbers so real values are not shown
Should not be trend charts since that often leads to incorrect interpretations by the customer
Should be x-y plots or interval plots with statistical values like P-Value and/or R2 factor clearly shown
4. Validation test results (include if any have been done)
5. Other investigation action results that have been completed
6. Path forward
A detailed investigation plan with prioritized actions that have target completion dates shown
Step 6 & Onward: Publish Initial Customer Data
Package
39. 39
Craig A Zedwick June 2016
• Root cause investigations are usually complex and require focus
and time from many people
• Every customer issue will be different, so every investigation will
differ
o But the actions listed in this training should be done every time an
issue arises where our customer requires support
o This format can also be used for internal root cause analysis
o After initial data package is complete, the rest of the investigation will
be unique to each customer issue, so no fixed activity list can be used
• Our customers need to see that we can control our own
process/product and quickly solve problems when they arise
o If we don’t show them that we are skilled, they will impose their own
controls or go to other suppliers
o We need to build trust with our customers that we are the experts
when it comes to our product or service
Summary
Editor's Notes
The complaint background information forms the foundation of the problem statement
Digging deeper allows the customer liaison to understand if the customer has changed anything on their end that could impact the investigation
Sometimes customers will try to compensate for a performance issue by making changes
This makes sense to the customer, but confuses the data that they provide because there are now two data sets
If this is true, sometimes understanding what the customer did in their process will allow the investigator to adjust the data after the adjustment to be comparable to the data before the adjustment
In this way, a trustworthy set of customer data can be compiled for use in the investigation
Not every problem is always 100% due to our product, so it is important to take some time to look for any other contributing factors
This is not an excuse to avoid investigating, but rather a way to make sure that you properly understand how your product may interact with another product or the customer’s process to result in a failure.
A coincidence between lot change and defect onset does not mean the new lot is the root cause – only that we should investigate the new lot first
Without knowing the amount of each RM lot used, we might conclude that this RM is not a signal because the known-good lot was used
This is also critical because we often need to do calculations where RM data must be weighted according to the percent of each RM lot used in production
Blaming RMs seems easy because we can say that it isn’t our fault, but often that creates more uncertainty in our customer’s minds. We need to have data and validation for any root cause.
1. Completed fishbone diagram can be a powerful exhibit to the customer to show that our investigations are complete and exhaustive
2. Splitting brainstorming and screening into separate meetings allows people to think about the ideas listed before they need to screen ideas and prioritize actions
1. Correlation does not prove cause-effect relationship, just points to variables that have higher probability of being the root cause (or connected to the root cause in some way)
2. Validation testing should be done as follow-up once the statistical analysis identifies possible root causes
-- Could include internal polish testing or customer pi-runs
Leave room between good and bad number assignments in discrete data in order to give some distance between points in case future feedback has marginal behavior between good and bad
If more than one performance feedback data set is given, then create separate worksheets to analyze separately
Array Example: the filter DP values for each lot are either associated with a good lot or a bad lot. Use Array1 for those lots that are good and Array2 for those lots that are bad.
The “3” as the last input value tells the function that the two arrays do not have identical variances, so this should always be kept at the value of “3”
If the P-Value is less than 0.05, then there is a 95% chance that there is a true difference between the mean value of that parameter for the good lots compared to the mean value for the bad lots
This does not prove that this parameter is the root cause, but it eliminates those variables where the P-Value is greater than 0.05
In Excel, generate a t-test P-value for each parameter
Use function =t.test(array1,array2,number of tails,3)
Arrays 1 & 2 represent the parameter data for good and the parameter data for bad
Value inputted for number of tails is usually “2”
If distribution is one-sided (e.g. data where some portion of data is at or below detection limit) then input “1” for number of tails
Enter function at the bottom of the 1st column of data and fill to the right for all columns
The resulting set of values will represent the P-Value statistic for the data in each column
Low P means high chance of a difference between good and bad
Correlation does not mean root cause – two variables can move together and be linked, but not have one variable causing the other
Correlation does not mean significance – two variables could form a very linear relationship, but if the slope of the line is very small, then that means that the impact of the CMC parameter on customer performance is insignificant
In Excel, generate a correlation factor for each parameter
Use correlation function in data analysis add-in or use function =correl(y-values,x-values)
Y-values should be the customer performance data
X-values should be the CMC data from the parameter being studied
Enter function at the bottom of each column of data and fill to the right for all columns
Output is a set of linear correlation coefficients (R) – one for each column of CMC data
Correlation coefficient describes how closely the data fits a straight line
R < 0.2 no linear relationship
R between 0.2 and 0.6 some connection, but not direct or may be convoluted
R > 0.6 a good linear relationship that should be investigated
For parameters with R of >0.6, a x-y scatter plot is the best way to present the data
This can be done in Excel or in Minitab
Minitab has the advantage of being able to generate a P-Value statistic and the R2 value
This can help indicate if the correlation is significant or not