Managing Coding Operations
Section B
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Creating Batches
• Homogeneity
– Alike items within a batch
– Helps to keep samples representative
• Batch Size
– Rule-of-thumb: ½ to 1 day of work
– Very small batch frequent QC, more paperwork
– Very large batch delayed feedback, more rework
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Returning Materials from the Field
• What needs to be returned from the field?
• How should these items be packed and sent, including
control forms?
• Provide field staff with instructions and materials for
proper returns
• Develop tracking system to verify completeness of
returns at each level
• Develop receipt, unpacking and check-in procedures
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Storage Room Operations
• Check-in should include geographic area, number of
forms, and other materials by EA (map, listing sheets)
• These materials are grouped by batch, and given a
batch ID that corresponds to a geocode
• Batches are shelved and tracked through processes
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Acceptance Sampling Plan
The process of accepting or rejecting a lot (batch)
of work by inspecting a sample selected
according to a predetermined sampling plan
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Acceptance Sampling Risks
• Producer’s risk (Type I error)
– Rejecting good batches
• Consumer’s risk (Type II error)
– Accepting bad batches
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Operating Characteristic (OC) Curves
• OC Curves characterize acceptance sampling
plans.
• OC Curves are graphical representations for the
probability of acceptance (Pa) for every possible
number of errors in a batch (p).
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Example OC Curve
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C=12, N=400
0.8
0.6
Pa
C=6, N=200
0.4
0.2
0
1
2
3
4
incoming percent defective
5
6
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Increasing Sample Size
1
n=400, c=2
0.8
n=240, c=2
0.6
Pa
n=80, c=2
0.4
0.2
0
0.02
0.04 fraction 0.06
incoming
defective
0.08
0.1
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Varying Acceptance Number
1
0.8
n=110, c=2
0.6
n=110, c=1
Pa
0.4
n=110, c=0
0.2
0
0.02
0.04 fraction 0.06
incoming
defective
0.08
0.1
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Acceptance Sampling Trade-Off
• Sampling Size vs. Acceptance Criteria
– Assuming a set quality level, we can make choices
regarding inspection rates and acceptance criteria
– To decrease inspection rate, we must tighten
acceptance criteria
– To allow more defects, we must increase sample
size
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Acceptance Sampling Inspection
• Start with 100% inspection and appropriate acceptance
number for level of quality
• When a batch passes, reduce inspection on that coders
work to sample inspection
• If sample inspection fails, return to 100% inspection
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100% Dependent Acceptance Sampling
• Assign a coder’s completed batch to a verifier
• Verifier reviews all questionnaires and writes codes
on separate form when they don’t agree with coder
• Supervisor compares the two and decides correct
code when the coder and verifier codes differ
• An error is attributed to the coder/verifier not chosen
as correct and the batch is either passed or failed
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Sample Dependent Acceptance Sampling
• Verifier uses a random number table to choose the
first questionnaire to review
• Verifier reviews all nth questionnaires afterwards
until the entire batch is completed
• The supervisor then checks the sample, attributes
errors and either passes or fails the batch
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Independent Acceptance Sampling
• Assign a batch to a verifier before it is coded
• Verifier codes questionnaires on separate form
• Batch is coded by coding clerk
• Completed batch and verifier forms are checked
by supervisor who attributes errors and either
passes or fails the batch
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Coding Staff Review
• Coding clerks
– Percentage increase for verification
• Supervisors as a ratio to coders
– Remember verification review work
• Assignment clerks
• Overall shift supervisors
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Fighting Coding Boredom
• Scheduled breaks
• Rotation of duties
• Working in shifts
• Working environment
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Staff Incentives
• Performance based
• Clear criteria for incentives
• Avoid across the board incentives
• Public recognition
• Non-monetary gifts
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Transitioning Production Staff
• Are there subsequent activities where these staff
would be useful?
• Can choose the best staff based on operational
records
• Saving on recruitment could be transferred to
training and other activities
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Section B Quiz
1.
2.
3.
4.
What characteristics should batches have?
When do you plan for return of materials?
What is an acceptance sampling plan?
What does an operating characteristic curve
describe?
5. Describe the use of multiple inspection
methods in verification.
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