Quality Improvement

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Quality Improvement
Introduction to Business Statistics, 5e
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Definitions

• Quality product or service A product or
  service that meets or exceeds the
  expectations of the customer.
• Process Any combination of people, machinery,
  material, and methods that is intended to
  produce a product or service.
• Quality Characteristics Features of a product
  that describe its fitness for use .

Introduction to Business Statistics, 5e
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Definitions

• Statistical Process Control (SPC) The
  application of statistical quality-control
  methods to measure and analyze the variation
  found in a process.
• Control Chart A statistical chart used to
  monitor various aspects of a process and to
  determine if the process is in control or out of
  control.

Introduction to Business Statistics, 5e
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Malcolm Baldrige National Quality Award Criteria

• Leadership System
• Strategic Planning
• Customer and Market Focus
• Information and Analysis
• Human Resource Focus
• Process Management
• Business Results

Introduction to Business Statistics, 5e
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Quality Improvement Tools

• Flowcharts
• Cause-and-Effect Diagrams

Introduction to Business Statistics, 5e
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Flowchart
Figure 12.2
Introduction to Business Statistics, 5e
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Cause-and-Effect Diagram
Introduction to Business Statistics, 5e
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Figure 12.3
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Process Variation and Control Charts Sources of
Variation

• Machinery
• People
• Materials
• Production Methods
• The Environment

Introduction to Business Statistics, 5e
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Deming Funnel Experiment Strategies

• Strategy 1 Do not react to this random
  variation and do not move the funnel.
• Strategy 2 Measure the distance from the
  marbles resting place to the bulls-eye.
  Move the funnel and equal distance, but in the
  opposite direction.

Introduction to Business Statistics, 5e
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Deming Funnel Experiment Strategies

• Strategy 3 Measure the distance from the
  marbles resting place to the bulls-eye.
  Move the funnel this distance, in the opposite
  direction, starting at the bulls- eye.

Introduction to Business Statistics, 5e
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Deming Funnel Experiment
Introduction to Business Statistics, 5e
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Figure 12.5
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Control Charts

• A process is in control if the observed variation
  is due to inherent or natural variation. This
  variability is the cumulative effect of many
  small, essentially uncontrollable, causes.
• A process in out of control if a relatively large
  variation is introduced that can be traced to an
  assignable cause.

Introduction to Business Statistics, 5e
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General Form of a Control Chart
Introduction to Business Statistics, 5e
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Figure 12.6
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Control Chart
Introduction to Business Statistics, 5e
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Figure 12.7
15
X and R Charts
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X and R Charts
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X and R ChartsProcess for Estimating ?

• Determine the average of the m values of R.
• Select the values of d2 from Table 12.3 using the
  corresponding sample size, n.
• Estimate ? using

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X and R ChartsControl Limits
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X and R ChartsControl Limits
Introduction to Business Statistics, 5e
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Figure 12.9
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R Chart
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R Chart
By defining
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Steps for Making X and R Charts

• Collect m samples of data, each of size n.
• Compute the average of each subgroup.
• Compute the range for each subgroup.
• Find the overall mean.
• Find the average range.
• Estimate ?.

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Steps for Making X and R Charts

• Compute the 3-sigma control limits for X.
• Compute the 3-sigma control limits for R
• Construct the control charts by plotting X and R
  points for each subgroup on the same vertical
  line.

Introduction to Business Statistics, 5e
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Pattern Analysis for X
Figure 12.12
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Minitab X Chart
Introduction to Business Statistics, 5e
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Figure 12.13
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Control Chart for the Proportion Nonconforming
The p chart

• Reasons for Using a p Chart
• Quality measurements are not possible.
• Quality measurements are not practical.
• Many characteristics on each part are being
  judged during inspection
• The main question of interest is will the
  process be able to produce conforming products
  over time?

Introduction to Business Statistics, 5e
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Steps for Making p Charts

• Collect m samples of data, each of size, n.
• Determine the proportion nonconforming for each
  sample.
• Find p, the overall proportion nonconforming.
• Compute the 3-sigma control limits
• Draw the control lines and plot the values of pi.

Introduction to Business Statistics, 5e
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p Chart Equations
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p Chart for Ex. 12.3
Introduction to Business Statistics, 5e
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Figure 12.17
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The c Chart Construction

• Collect m samples of data, each of size, n.
• Determine the number of nonconformities for the
  ith unit. Call this value ci.
• Find the average number of nonconformities per
  unit, c.
• Compute the 3-sigma control limits.
• Construct the chart.

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c Chart Equations
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Process Capability

• Specification Limits process requirements
• Lower spec limit (LSL) the lower limit of the
  process output that meets the process
  requirements.
• Upper spec limit (USL) the upper limit of the
  process output that meets the process
  requirements.

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Process Capability
Figure 12.20
Introduction to Business Statistics, 5e
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The difference between 12.01 and 12.19 is
referred to as the process spread.
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Process Capability
Introduction to Business Statistics, 5e
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Figure 12.21
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Process Capability Ratio Cp

• Assumptions
• The process is centered within specifications.
• The process is normally distributed.
• The process is stable.

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Cp
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Process Capability Ratio Cpk

• Assumptions
• The process may or may not be centered in spec.
• The process is normally distributed.
• The process is stable.
• Control charts will be used to monitor the
  process over time.

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Process Capability
Introduction to Business Statistics, 5e
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Figure 12.22
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Procedure for Finding Cpk
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Process Capability
Introduction to Business Statistics, 5e
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Figure 12.23