Testing for Process Confidence - Sample Size

M

Mark Smith

#1
Here's the problem.

I want to know how many pieces from some process I need to test (and what the acceptable failure number would be) if I need the process to produce pieces with 95/95 confidence and reliability and I know nothing else about the process. If any failure occurs, how many additional pieces must be tested to achieve the same level of confidence and reliability? I believe I would begin by testing 60 pieces and allow zero failures to achieve this goal. Am I right? explain!
 
Elsmar Forum Sponsor
D

Don Winton

#2
I apologize for the delayed response. I have 'computerless' at work and the one at home is sorta acting up. Work is OK now and I will have an answer to your request in a day or so. Again, my apologies.

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
D

Don Winton

#3
There is an extensive discussion on sampling, confidence, sample sizes, etc at:

Sampling Plans

Read thru this and if you any more questions, please ask.

Regards,
Don
 
D

Don Winton

#4
Mark Smith Wrote:

Don,

"Thom R Nichols" wrote an article in the June 1997 issue of MDDI Magazine ( Assessing Pass/Fail Testing When There Are No Failures to Assess )that provides a plan for assessing pass/fail testing when no failures occur. Using his chart, I selected 60 samples with zero rejects for 95% confidence. The question is "If a failure occurs, how many additional units need to be tested over 60 with zero additional failures for me to have the same level of confidence in the process producing the product in question?" Can you explain it to me? My statistical background is very limited.

Now I understand the question, I think.

You selected 60 samples with 95% confidence, therefore, from Table I, you were expecting a long term failure rate not to exceed 6.0%. But you had one failure. Now, how many additional units do you have to test to achieve the same 6.0% long term failure rate? Is that it? Let us assume it is.

From Table I, if you test 100 units with one failure, the long term failure rate is predicted to be 5.4%, which is 0.6% less than your original expectation of 6.0%. Therefore, I would test an additional 40 units, and with zero failures, your long term failure rate is predicted to be 5.4%. If the additional 40 units also had one failure, then you would need to work on the process and try the procedure over, based on the info presented in the article. Of course, you could always predict long term failure based on the actual failures. But, that is another story. Test the next 40 and if there are additional failures, we can discuss it then.

Can you explain it to me?
Not really. While I understand why they are presenting this information, I do not know how they derived the charts. The authors chose not to present the statistical theory and I do not have access to references 1 or 2. If you know where they can be found on the web, let me know. My local library sorta sucks in this department. Sorry.

Regards,
Don
 
Thread starter Similar threads Forum Replies Date
J Microbiology Testing - Managing a Microbiology Process Hospitals, Clinics & other Health Care Providers 2
R Testing a Product Recall Process IEC 27001 - Information Security Management Systems (ISMS) 8
Sam Lazzara Lot Release Testing versus Process Validation Studies Qualification and Validation (including 21 CFR Part 11) 9
M Manufacturing Process Validation Destructive Testing Sampling Plan Advice Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
C Safety Tests Required for In-Process Testing of Medical Devices IEC 60601 - Medical Electrical Equipment Safety Standards Series 2
B Pouch Sealing and Peel Testing Process Improvement ISO 13485:2016 - Medical Device Quality Management Systems 10
M Application of Special Process - Validation and FAI in Wind Tunnel Testing AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
A Testing Process Audit - Defining a Process Compliance Mechanism Software Quality Assurance 2
Q Process Impact Validation Testing - Polishing process Capability, Accuracy and Stability - Processes, Machines, etc. 2
J Process FMEA in a testing facility IATF 16949 - Automotive Quality Systems Standard 9
J Process Audit questions on Ultrasonic and Resonance testing Process Audits and Layered Process Audits 4
C Is Parts/Process Average Testing SPC by Another Name? Statistical Analysis Tools, Techniques and SPC 3
C Laboratory Testing as a "Special Process" - element 7.5.2 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 4
M Polyurethane Foam Testing and Controlling the Foaming Process Manufacturing and Related Processes 6
A How do you structure your IC Assembly and Testing PFMEA (Process FMEA)? FMEA and Control Plans 10
D Testing process is non value added process under TS16949? IATF 16949 - Automotive Quality Systems Standard 1
R GB9706.1:2020 - in-country testing China Medical Device Regulations 0
A Bench Testing US Food and Drug Administration (FDA) 2
R Validation of Software used in Verification Testing ISO 13485:2016 - Medical Device Quality Management Systems 2
M Do i need to have equipment validation if 100% testing is completed? Qualification and Validation (including 21 CFR Part 11) 4
E Biocompatibility testing of our applied part seems redundant Other Medical Device Related Standards 2
A Recommended testing methods for weather stripping Manufacturing and Related Processes 6
T Shrinkage Testing for EPDM Material Various Other Specifications, Standards, and related Requirements 5
J Managing design verification regression testing of design changes Design and Development of Products and Processes 1
D Conductivity Water Samples testing temperature Qualification and Validation (including 21 CFR Part 11) 2
G Pricing Structure for Physical Mechanical Testing of Labs Manufacturing and Related Processes 1
S Skipped/Reduced testing in Pharma for Raw materials and Intermediates Manufacturing and Related Processes 0
S Pharmaceutical Shelf Life Testing Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 0
D How to testing of Pressure relief valve as per API 6D ? Oil and Gas Industry Standards and Regulations 1
J Impact Testing--Is conversion between Izod and Sharpy Possible? General Measurement Device and Calibration Topics 3
O Should a Covid vaccine and testing policy be included as part of ISO9001 or AS9100 risk management? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
V How to select the tests for proficiency testing Measurement Uncertainty (MU) 0
B Customer Preference Testing Customer and Company Specific Requirements 2
N Pre-Clinical Performance Testing Design and Development of Products and Processes 3
I Software (SaMD) mobile application verification testing: objective evidence Medical Information Technology, Medical Software and Health Informatics 2
I How to find required testing for a specific device? Other US Medical Device Regulations 3
J CQI-9v4 Alternative TUS Testing Methods Various Other Specifications, Standards, and related Requirements 0
M ASTM F1717 Static and Dynamic Testing 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
T Mold Limits for Microbiology Testing Other Medical Device Related Standards 3
S Orthopedic implant sterility testing Medical Device and FDA Regulations and Standards News 1
H Independence between the development and testing IEC 62304 - Medical Device Software Life Cycle Processes 6
M Issues with leakage current testing for a CLASS II device since no PE and FE is present IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
M Testing criteria - where to place Design and Development of Products and Processes 2
E 60601-1 - Tilt testing - Tensile safety factor IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
V Setup for testing against ISO14708 clause 16 (protection of the patient from herms caused by heat) Other Medical Device Related Standards 0
gramps What do you think about automated QA testing For software app industry? Misc. Quality Assurance and Business Systems Related Topics 5
B In house NIOSH pre Testing accepted by NIOSH? US Food and Drug Administration (FDA) 1
M Bacteriostasis/Fungistasis Testing Other Medical Device and Orthopedic Related Topics 6
P Sample Size for Distribution Simulation Testing Inspection, Prints (Drawings), Testing, Sampling and Related Topics 11
N EN 813, EN 12277, EN 1497 - Testing some harness prototypes to an EN standard Various Other Specifications, Standards, and related Requirements 0

Similar threads

Top Bottom