STEP #2 - MEASURE
DATA & SAMPLING
Step #2 - MEASURE
In the Define phase a team charter was produced,
an overview of the process to be improved, and
information was established on what is critical to
quality of the customers. Probably the largest
segment of information is within this step. In this
phase, the goal is to pinpoint the location or
source of the problem as precisely as possible by
building a factual understanding of existing
process conditions and problems. Having this
knowledge will assist you in narrowing the range
of potential causes that are needed to investigate
in the Analyze phase. Therefore, the important
function of the MEASURE phase is to establish a
baseline capability level. The tools that are most
commonly utilized in the Measure phase are:
1.
Data Collection Plan
2.
Data Collection Forms
3.
Control Charts
4.
Frequency plots
5.
Gage R&R
6.
Pareto Charts
7.
Prioritization Matrix
8.
Failure Mode and Effects Analysis
9.
Process Capability
10.
Process Sigma
11.
Sampling
12.
Stratification
13.
Time Series Plots (Run Charts)
In some cases, where I have these items already
available on this web site, I will direct you back to
the place on this web site where this tool can be
found. If the context of the tool is not logical
within this segment, I will also direct you to
another page within this web site rather than take
up extensive room on this phase space. In both
cases, watch for a notation that states, "For an
Example, Click Here" that will direct you to the
relevant tool.
DATA COLLECTION
In planning for data collection it is important to:
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Be able to identify possible measures.
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Know how to select the most important
variables to measure.
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Know how to create a data collection plan.
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Be able to identify stratification factors for a
given problem.
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Know the various types of data available.
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Be able to create and use operational
definitions.
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Be able to create a useful data collection
form, whether variable or attribute.
Desired data characteristics need to be:
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Sufficient
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Relevant
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Representative
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Contextual
One of the most important things a team can do
in planning for data collection is to draw and label
the graph that will communicate the findings
properly before the collection process begins. This
points you to exactly what type of data you will
need; that is, in order to be able to effectively
collect data, you have to know what it is you are
trying to illustrate. Additionally, it also raises
questions that you may not have considered and
need to add to your plan.
Some of the types of data collection forms that
you can use are here on this web site at:
Recording what data you are going to collect
reminds you what you want to accomplish. Noting
the type of data
helps you decide how you
should analyze the data. An operational definition
defines exactly how you will go about collecting
and recording the data.
How will you ensure consistency?
What will you do to make sure the data collected
at one point in time is comparable to the data
collected at other times to ensure that there is no
bias introduced to skew the results or give a false
impression of the overall problem plan.
What is your plan for starting data collection?
Just how will you go about collecting the data?
Thinking about how you will display the data will
help you make sure you are getting the right kind
of data to answer the question you have in mind.
See Section on CheckSheets - Click Here.
IDENTIFY KEY MEASURES & CLARIFY GOALS
The goal here is to make sure that the data you
collect will give you the answers that you need.
The "right" information: describes the problem
you're studying; describes related conditions that
might provide clues about causes; can be
analyzed in ways that answer your questions.
In the equation Y = f(X1, X2, X3, . . . . . Xn), Y relates
to the process output. It tells us how well we are
meeting customer needs. X relates to the various
input and process variables. You need to gain this
knowledge in order to improve the process.
Understanding the variation in the output variable
(Y) requires data relative to the X's. Since data
collection can consume a tremendous amount of
time, it is critical to focus on the key measures.
The high-level SIPOC map provides a starting
point for identifying possible measures.
Prioritization Matrix - There are two applications
for a prioritization matrix:
1.
Linking out variables to customer
requirements, and
2.
Linking input and process variables to
output variables.
The second application is used for identifying key
measures.
Why use a prioritization matrix?
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To identify the critical few variables that
needs to be measured and analyzed.
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To help to focus the data collection effort.
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To help formulate theories about causes
and effects.
When to use a prioritization matrix:
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There are too many variables that might
have an impact on the output of the
process.
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Collecting data about all possible variables
would cost too much time and money.
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Team members have different theories
about what happens in the process.
How to construct a prioritization matrix:
1.
List all output variables.
2.
Rank and weight the output variables.
3.
List all input and process variables.
4.
Evaluate the strength of the relationship
between output and input/process
variable (correlation factor).
5.
Cross-multiply weight and correlation factor.
6.
Highlight the critical few variables.
F M E A
Failure Mode and Effect Analysis (FMEA) is
another tool that can be used to help focus on
data collection efforts for the input and process
variables that are critical for the current process.
Therefore, it can be used in the Measure phase as
well as the Improve phase since it is a structure
approach to identify, estimate, prioritize and
evaluate risk. The entire purpose of the FMEA is to
prevent failures from occurring, and what the
effects are should a failure occur.
Why use an FMEA?
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Identifies the critical input and process
variables that can affect output quality.
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Establishes priorities and guides the data
collection effort.
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Evaluates the risk associated with defects.
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Helps to formulate assumptions about the
relationship between variables.
When to use an FMEA?
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Lack of clarity about what the important
variables are and how they affect output
quality.
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Need to prioritize data collection efforts.
How to Construct an FMEA:
1.
Identify potential failure modes - ways in
which the product, service, or process
might fail.
2.
Identify potential effect of each failure
(consequences of that failure) and rate the
severity.
3.
Identify causes of the effects and rate their
likelihood of occurrence.
4.
Rate you ability to detect each failure mode.
5.
Multiply the three numbers together to
determine the risk of each failure mode
(RPN = Risk Priority Number).
6.
Identify ways to reduce or eliminate risk
associated with high RPN numbered items.
You can download a sample FMEA form in Adobe
format (.pdf), as well as other information and
books on FMEA's, from:
http://www.fmeainfocentre.com
The next question you might ask yourself is how
does one determine what numbers are to be
placed into the boxes for Severity, Occurrence and
Detection? Are they just random numbers
selected without rhyme or reason? Not at all, the
Automotive Industry Action Group (AIAG) has
created an FMEA manual that is linked to ISO9001:
TS16949 standards, and within that book are
tabled guidelines for how to determine the
correct number to place in each segment,
predicated on certain criteria. I have placed a
sample FMEA (CLICK HERE) for your review and
understanding.
At this next link, ( R P Ns) CLICK HERE you will find
the tables that list the criteria for each of the
categories mentioned above, to enable you to
decide how to place the RPN numbers in each
category. If you have further questions regarding
FMEA number assignments, you may visit FMEA
Info for clarification or further knowledge.
Stratification - dividing data into groups (strata)
based upon key characteristics. A "key
characteristic" is some aspect of the data that you
think could help explain when, where, and why a
problem exists. The purpose of dividing the data
into groups is to detect a pattern that localizes a
problem or explains why the frequency of impact
varies between times, locations, or conditions.
Ways to stratify date - typically the data groups
are based upon:
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WHO - which people, groups of people,
departments or organization are involved.
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WHAT - machines, equipment, products,
services, suppliers.
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WHERE - physical location of the defect.
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WHEN - time of day, day of the week, step of
the process.
In the Analyze phase, you will see how to analyze
stratified data. By visiting the CHECK SHEET
examples within this web site, you will see how
you can stratify data as you collect, and thus give
a visual representation indicating where the
problems lie while representing your data in a
graphical form. There are basically two types of
data:
1.
Continuous Data - often obtained by the use
of a measuring system. The usefulness of the data
depends on the quality of the measurement
system. Counts of non-occurrences are best
treated as continuous data.
2.
Discrete Data - includes percentages,
counts, attributes and ordinals. Percentages equal
the proportion of items with a given characteristic;
need to be able to count both occurrences and
non-occurrences. For count data, it is impossible
or impractical to count a non-occurrence; the
event must be rare. Occurrences must be
independent.
Some Examples for Data Stratification are:
Continuous or "variable" - Measuring instrument
or calculation
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Service - elapsed time to complete
transaction, average length of phone call
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Manufacturing - elapsed cycle time, gauge
production rates, weight, length, speed
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Both - budget vs. actual in dollars; average
customer satisfaction score; amount
purchased
Discrete: Percentage or Proportion - Count
occurrences and non-occurrences
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Service - proportion of late applications,
incorrect invoices.
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Manufacturing - proportion of defective
items, reworked items, damaged items,
late shipments
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Both - proportion of employees absent,
incomplete orders
Discrete: Count - court occurrences in an area of
opportunity
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Service - number of applications, errors,
complaints, etc.
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Manufacturing - number of computer
malfunctions, machine breakdowns,
employee accidents, etc.
Discrete: Attribute - observations
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Service - type of applications or type of
requests
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Manufacturing - type of products or defects
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Both - type of customer, type of method
used, location of activity
Discrete: Ordinal - observation or ranking
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Both - customer rating (scale of 1 to 5); day
of the week (M-F); date, time order
OPERATIONAL DEFINITIONS
The next step in data collection is to develop
operational definitions and procedures. The goal
is to make sure all the data collectors measure a
characteristic universally, that is, in the same
manner and method. This prevents variation and
confusion in the measurements. An operational
definition is a precise description that explains
how to get a value for the characteristic that you
are trying to measure and record. It includes what
something is and how it should be measured. The
features you want to include in an operational
definition are:
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Must be specific and definable in simple
terms
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Must be measurable, whether a variable
measurement or an attribute
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Must be useful to both you and your
customer, and therefore quantifiable
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There is no single right answer, it is
measured how it is - within or outside of
specification; pass or fail; go or no-go.
The more specific the definition is, the better the
results will be. Plan on refining the definition after
you try it out. Have those who are going to do the
measuring read the definition and ensure they
understand what the measurement results are to
be and how to properly obtain the measurements
you want to get. If you collect the data manually,
you will need to train the data collectors
consistently to ensure the measurements are
made in the same way. With calipers, for instance,
there is always the variable of whether it is a tight
or loose fit. The same applies to pin gauges; is it
to be a snug fit or loose fit?
DATA COLLECTION FORMS - Check sheets are
basic forms that help standardize the data
collection process by providing specific spaces
where people are to record the data. Again, I refer
you to the Check Sheet page within this web site
for a better understanding and sample format. By
viewing this Check Sheet site, you can see the
different types of check sheets that are available,
depending upon the type of measurement you set
out to accomplish.
A FREQUENCY PLOT check sheet is a special type
of check sheet that is used to record for numerical
data. As you plot, you are actually creating a
picture that shows how often different values
appear.
Another type of check sheet that can be used that
is not on this web site is a Confirmation Check
Sheet. This is a special type that is used to confirm
that steps in a process have been completed and
to collect the data on time taken in different
process steps. An Example is given below:
CONTINUE TO PART TWO OF MEASURE NEXT- -
PART TWO
© The Quality Web, authored by Frank E. Armstrong, Making Sense
Chronicles - 2003 - 2016