# What Sample Size for Destructive Test and is 'T' Test applicable?

M

#### Magus

I have a product that runs ~900 pcs per lot.
I have been running a destructive pressure test using a sample of 53 pcs per lot to try and show process capability. Sample size of 53 was derived from an 0.65 AQL sample c=0 as my initial sample size.

The mean of my sample test have been running ~1800 psi with a std dev of ~100 psi. I am trying to show that my total distribution is above a lower test limit of 1200 psi. (+/-6 sigma process). If 1 part of the sample tests below 1200 psi the lot is put on hold.

I am concerned about low side outliers. 450 psi is my customer’s high side failure threshold.

My amateur statistician is analyzing my work using a “T” Test. He states I can reduce my sample size to 7 pcs. Calculate the mean of the sample. If the sample mean of the 7 pcs is above 1500 psi the lot is OK.

I do not understand this application of the T Test. Is this valid and is the sample size of 7 correct?

Thanks,
Magus

U

#### Umang Vidyarthi

I have a product that runs ~900 pcs per lot.
I have been running a destructive pressure test using a sample of 53 pcs per lot to try and show process capability. Sample size of 53 was derived from an 0.65 AQL sample c=0 as my initial sample size.

The mean of my sample test have been running ~1800 psi with a std dev of ~100 psi. I am trying to show that my total distribution is above a lower test limit of 1200 psi. (+/-6 sigma process). If 1 part of the sample tests below 1200 psi the lot is put on hold.

I am concerned about low side outliers. 450 psi is my customer’s high side failure threshold.

My amateur statistician is analyzing my work using a “T” Test. He states I can reduce my sample size to 7 pcs. Calculate the mean of the sample. If the sample mean of the 7 pcs is above 1500 psi the lot is OK.

I do not understand this application of the T Test. Is this valid and is the sample size of 7 correct?

Thanks,
Magus
There is a similar discussion at 'This Thread' .

Umang

#### Bev D

##### Heretical Statistician
Super Moderator
a t test is a test of means. it is used to compare either two means to each other or a single mean to a target value to determine if the mean(s) are statistically significantly different from each other.

It appears that your statistician is saying that as long as the mean of your sample is 3 SDs gretaer than your lower spec limit you have an acceptable lot.

it is not clear hwo he determined a sample size of 7

this approach may work but we would need to see your historical data first. can you post it in excel in time sequence?

A Destructive Test Sample Size Reduction Statistical Analysis Tools, Techniques and SPC 10
A Destructive Test Sample Size Determination Statistical Analysis Tools, Techniques and SPC 4
C Batch Acceptance: Cpk requirements and Sample Size - Destructive Testing Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
C Sample Size in Destructive Pull Test and Interpretation of Test Result IATF 16949 - Automotive Quality Systems Standard 5
Sample size calculation for the medical device with multiple indications. e.g. suture US Food and Drug Administration (FDA) 3
Sample Size rationale to reduce size and use special levels EU Medical Device Regulations 6
Gage Pin Sets? Calibrate/Verify them all or just a sample size? General Measurement Device and Calibration Topics 22
How to determine sample size to test when the acceptance criteria is x >= Standard value? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 7
Sample size calculation Using Minitab Software 3
What Theory is MIL-STD-105E Sample Size Code Letters Based on? Quality Tools, Improvement and Analysis 3
FMEA link to Control Plan frequency and sample size FMEA and Control Plans 20
Noob question regarding sample size Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
Help needed in choosing the method of calculating the minimum sample size Internal Auditing 12
Estimate Sample Size for very rare event Using Minitab Software 1
Determining Sample Size and Method Quality Tools, Improvement and Analysis 12
Complaint Return Sample Size Question 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 4
Frequency and sample size for lot release of EtO sterilized products EU Medical Device Regulations 2
Clinical assessment sample size - Medical device Class IIb implantable (93/42 directive) EU Medical Device Regulations 2
Sample Size for Distribution Simulation Testing Inspection, Prints (Drawings), Testing, Sampling and Related Topics 11
Stress / Challenge Conditions for Design Verification Testing to Reduce Sample Size 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 11
How can Acceptance Number and Reject Number be larger than Sample Size on Z1.4 Table? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
Validation Sample Size for Tray Seal Qualification and Validation (including 21 CFR Part 11) 4
Design Verification Sample Size vs Repeats Statistical Analysis Tools, Techniques and SPC 9
Minimum sample size - Guidance and statistical rationale Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
Unrealistic Packaging Validation Sample Size 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 41
Control chart for huge sample size Statistical Analysis Tools, Techniques and SPC 9
Is there a standard for sample size during R&D phase Other ISO and International Standards and European Regulations 18
Sample size definition in an Automotive SMT pilot lot run Misc. Quality Assurance and Business Systems Related Topics 1
Correct way to certify hydrostatic testing when it is not 100% (and Sample Size) Various Other Specifications, Standards, and related Requirements 6
Determining sample size for device sterility Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
Determining of sample size for 'Operational Qualification' AQL - Acceptable Quality Level 5
Bayes Success run Theorem for sample size during OQ&PQ Qualification and Validation (including 21 CFR Part 11) 4
Device modifications - Clinical sample size rationale EU Medical Device Regulations 5
Sample size for creating a data base as a reference to a tested variable Other Medical Device and Orthopedic Related Topics 6
T Sample Size for Design Validation Design and Development of Products and Processes 4
C AS9138 Sample Size Determination AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
Acceptable maximum RSD (relative standard deviation) for an sample size Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
E Sample size for design verification of variable in single use device Design and Development of Products and Processes 20
R Sample size for clinical validation/investigation EU Medical Device Regulations 4
Process Validation sample size selection Statistical Analysis Tools, Techniques and SPC 0
J Interesting Discussion Sample Size Determination for Medical Device Other Medical Device and Orthopedic Related Topics 19
P Is it possible to make an educated decision using a very very small sample size? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
Sample Size for Biocompatibility Tests Other Medical Device Related Standards 4
V Firmware Verification Testing & Sample Size Software Quality Assurance 1
Determining Sample Size for Medical Device Component Validation Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
S Surveillance Sampling Test - Determining Sample Size Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
Sample Size Calculation (Confidence Interval and Reliability) - Medical Devices Reliability Analysis - Predictions, Testing and Standards 9
P Cleaning and Disinfection Validation Sample Size of 3? Other Medical Device Related Standards 2
Sample Size Calculation for Image Analysis - Microscopy Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
G Sample Size, Significant Figures, Scale General Measurement Device and Calibration Topics 3