Attribute sampling plan

Flyn17

Registered
In Attribute sampling plan, what is the allowable no of defects(c=?), if we were to inspect a lot size of 350k(all of them) with a confidence/reliability of 95/95?
What is the methodology used for this?

Mustapha

Starting to get Involved
What are you inspecting and what are you trying to accomplish? I can give you a basic run down, but it would help if you gave more info on what you're trying to do. Both sampling plans below have a confidence level of 95%

You can either use one of the standard sampling plans such as ANSI Z1.4 or Squeglia c=0. Most companies are moving towards Squeglia's c=0 sampling plans because it technically gives you the same result of the Z1.4 plans with less samples taken for measurement.

In your example, under Z1.4, under general inspection level 2 and an AQL of 1.0, your sampling code would be P and the number of samples you take would be 800. You could accept up to 14 defects within that 800 and only reject lot once you hit 15 defects. For c=0, you would take 90 samples and reject the lot on the first defect.

Bev D

Heretical Statistician
Super Moderator
You must state a RQL and/or AQL level in order to establish a c number.

BUT can you clarify your situation: you state “lot size of 350k(all of them). Do you mean you will inspect all 350k parts? Or are you going to sample randomly from a lot of 350k.

by the way, lot size is actually irrelevant despite some plans that index n based on sample size.

Are you looking for the formulas to use?

Flyn17

Registered
What are you inspecting and what are you trying to accomplish? I can give you a basic run down, but it would help if you gave more info on what you're trying to do. Both sampling plans below have a confidence level of 95%

You can either use one of the standard sampling plans such as ANSI Z1.4 or Squeglia c=0. Most companies are moving towards Squeglia's c=0 sampling plans because it technically gives you the same result of the Z1.4 plans with less samples taken for measurement.

In your example, under Z1.4, under general inspection level 2 and an AQL of 1.0, your sampling code would be P and the number of samples you take would be 800. You could accept up to 14 defects within that 800 and only reject lot once you hit 15 defects. For c=0, you would take 90 samples and reject the lot on the first defect.
I am inspecting cracks on a product. lets say, I have not done a IMV for this inspection and sold over 350k products, and found that we have 3 complaints due to the cracks. how do I support the statement, we are doing better in terms of Conf/reliability even if we were to validate the inspections.
AQL=.25% RQL=5%

Flyn17

Registered
You must state a RQL and/or AQL level in order to establish a c number.

BUT can you clarify your situation: you state “lot size of 350k(all of them). Do you mean you will inspect all 350k parts? Or are you going to sample randomly from a lot of 350k.

by the way, lot size is actually irrelevant despite some plans that index n based on sample size.

Are you looking for the formulas to use?
for validation AQL=.25% RQL=5%
Yes, inspect all of them
lot size is actually irrelevant despite some plans that index n based on sample size - did not understand this
formulas would help

Bev D

Heretical Statistician
Super Moderator
You don’t need a sampling plan - you need to calculate the confidence interval about the defect rate.

Flyn17

Registered
You don’t need a sampling plan - you need to calculate the confidence interval about the defect rate.
Could you help me with formula, on how to proceed to further

Bev D

Heretical Statistician
Super Moderator
Before formulas we need to understand the situation. The correct math matches the situation.
a few questions:
1. Do you inspect all parts for cracks? Or only a sample. If a sample what is the sample size and how did you decide on it?
2. How is the inspection done?
3. Have you performed an MSA on the inspection? If so what method did you use and what were the results?
4. And the most important question of all: what is the timing of the complaints? Are they randomly scattered throughout the 350k parts or are all they all from the same time frame / shipment & Customer / Lot & Customer? How many ‘good’ parts between teh complaints? There is a huge difference between 3 complaints over 350k parts and 3 complaints from the last 10 units shipped. Any math must take that into account.

Best Attribute Data Sampling Plan - Early Production Containment Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
W Sampling Plan problem - Determining Sample Size for both Attribute and Variables Data ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
D Attribute Sampling Plan help wanted Inspection, Prints (Drawings), Testing, Sampling and Related Topics 16
Applying Weibayes to Attribute sampling Reliability Analysis - Predictions, Testing and Standards 0
B IATF 16949 Cl. 8.6.6 - Acceptance Criteria - Zero Defects Attribute Data Sampling IATF 16949 - Automotive Quality Systems Standard 2
A Attribute Sampling Plans with Switching Rules - Software Recommendations Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
A AQL Tables or Binomial/Poisson Method? Attribute Sampling Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
G Attribute Data Inspection Sampling Matrix Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
A Sampling - Measuring and Inspecting a part with both Variable & Attribute Data Inspection, Prints (Drawings), Testing, Sampling and Related Topics 12
Q Is DPM defective parts per million a form of Attribute Data Sampling? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
Q ISO/TS 16949 Questions About clause 7.1.2. Attribute Data Sampling Inspection, Prints (Drawings), Testing, Sampling and Related Topics 11
U Zero Acceptance number procedure for Attribute Sampling Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
S SPC - Go/No Go Sampling - Attribute Data Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
J Acceptance Criteria for Attribute Data Sampling Plans shall be Zero Defects Inspection, Prints (Drawings), Testing, Sampling and Related Topics 14
Attribute MSA with limited test samples Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 0
Attribute Gage R&R with no bad samples Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
Comparing Two Test Variables Using Attribute Data Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
Question: How to analyze numerical and attribute data Reliability Analysis - Predictions, Testing and Standards 11
Attribute , for example C chart Statistical Analysis Tools, Techniques and SPC 16
MSA for attribute relation gage Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
Overwhelmed with attribute MSA requirement for visual inspection IATF 16949 - Automotive Quality Systems Standard 11
Need MSA 4th ed. compliant attribute MSA template General Measurement Device and Calibration Topics 4
Attribute Analysis for colour matching scale Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
Transform variable data into attribute data Reliability Analysis - Predictions, Testing and Standards 24
IATF & Attribute Study requirements IATF 16949 - Automotive Quality Systems Standard 9
Correct MSA study for an automated camera system which makes attribute inspection Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
Examples of Critical process parameter (CPP) and Critical quality attribute (CQA) Manufacturing and Related Processes 2
Template for Attribute Gage R & R wanted Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
B Easy Software Needed for Recording Mainly Attribute Data Quality Assurance and Compliance Software Tools and Solutions 2
A Does an attribute study (Go/NoGo pin gage) need two studies (1 for each pin) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
B Attribute Gage R&R study according to "Charbonneau" Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
R Can a Attribute Study be considered a Visual Inspection? Reliability Analysis - Predictions, Testing and Standards 6
MSA on Part Specific Attribute Fixtures Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
Gage Blocks: Attribute or Variable Gage? General Measurement Device and Calibration Topics 3
Attribute vs Variable Inspection Data ISO 13485 Requirement ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
D Calibration of a Width Gage Slot with an Attribute Gage - Maximum Width Condition General Measurement Device and Calibration Topics 16
R Visual Attribute Inspector Capability and KAPPA Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
D attribute gage RR in a unique way Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
M Proper Gauging - GD&T - Attribute gage to check true positioning on the shop floor Inspection, Prints (Drawings), Testing, Sampling and Related Topics 6
P RQL/AQL from Attribute Data Six Sigma 1
M Population failure rate based on attribute data Statistical Analysis Tools, Techniques and SPC 4
V Minitab - Attribute Gage Study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
Attribute G&R for all Visual Controls in Control Plan Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
J Attribute Test Method Validation 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
F MSA - Measurement System Analysis Attribute Data Crosstab sheet APQP and PPAP 1
B Bayes Success-Run on Attribute Data - Determining Sample Size Statistical Analysis Tools, Techniques and SPC 2
A Attribute Inspection P Chart Statistical Analysis Tools, Techniques and SPC 9
Do Attribute Control Charts really help? Statistical Analysis Tools, Techniques and SPC 9
S Visual Inspection Galvanized Attribute Study Quality Tools, Improvement and Analysis 2
Example of how to perform a Visual Attribute Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4