What is the 95 x 95 Inspection Level? Either an attribute or variables type plan

R

rschoi

#1
One is the so-called 95/95 requirement;
the other a 95% confidence interval on an average result.
A 95/95 type requirement may be met by either an attribute or variables type plan ;
the confidence interval on an average is met by a variables plan.

95/95 - Variables
We wish to be 95% sure that at least 95% (of the items being sampled) fall within the tolerance. To do this we project a frequency distribution and observe that it falls well within the required tolerance.
Tolerance limits which are a function of the sample size, sample average, and standard deviation are calcuated. These tolerance limits must be within the specification limits for acceptance.
Acceptance calculations are made as follows. For the sample size(n) an appropriate " K-factor" is found in a table. (An except from a table is shown below.)
n k
5 5.079
6 4.414
7 4.007
8 3.732
9 3.532
10 3.379
Let us assume that we are sampling 10 items to evaluate against a specification of 100 ¡¾10 pounds. An average of 104 pounds and a standard deviation of 2 pounds is calculated. The 95/95 limits are x-bar ¡¾Ks, or 104¡¾ (3.379) x (2) or 104¡¾6.758. The limits are 110.758 and 97.242 pounds. Since the 110.758 value is greater than the maximum requirement of 110, we would reject the lot.
As I know, The 95 limit is the confidence interval on an average.
The 95/95 limits are ......?


Thank you very much.


[This message has been edited by rschoi (edited 10 April 2000).]
 
Elsmar Forum Sponsor
D

Don Winton

#2
I know the 95% confidence level. But I don't know the 95% x 95% confidence level.

Frankly, I need more info. I have never heard of a 95% x 95% confidence interval.

Regards,

Don
 

Steve Prevette

Deming Disciple
Staff member
Super Moderator
#5
Marc said:
This is an 'Oldie', but has anyone heard of a 95 x 95 Inspection Level?
I have heard that in the context of "I am 95% confident that 95% of the parts being inspected are acceptable". Which is more of an attribute sample rather than a variable.
 
L

Lauren

#6
Marc said:
This is an 'Oldie', but has anyone heard of a 95 x 95 Inspection Level?
The sampling standards, are generally based on 95% confidence interval (that is why we cannot use them for some critical applications, such as Class III medical devices that might require the CI to be 99% or even higher!). That means that we accept the fact, that the sampling distribution is not exactly reflecting the populationand the mean of the sampling distribution may differ from the mean of the population up to 5%. At the same time the Type 1 (alpha) error, also known as producer risk and Type II (beta) error, also known as consumer risk need to be taken into consideration. The majority of scientific sampling plans are constructed with the assumption, that the producer risk (alpha) is 5% and it means that there is 95% probability that good product will be accepted and 5% probability that good product might be rejected by using the sampling plan. The 95% mean confidence interval and 95% probability of acceptance of good product by using the sampling plan is providing the 95X95 inspection plan, by using either ANSI/ASQ plans for attribute inspection, or C=0 plans, etc.. By the way, the sampling plans assume the consumer risk (beta) to be 10%, which means that 10% of bad product might be accepted by using the sampling plan
Hope it helps.

Lauren.
 
D

Dave Strouse

#7
Not so.

Lauren -

You said
"By the way, the sampling plans assume the consumer risk (beta) to be 10%, which means that 10% of bad product might be accepted by using the sampling plan
Hope it helps."


Sorry, but if you are talking about ANSI Z1.4 plans and AQL this is an absoulutely incorrect statement.

Look at the OC curves.
 

Tim Folkerts

Super Moderator
#8
Lauren,

95% chace of acceptance is a good rule of thumb, but when I looked closely, I discovered that even within a specific plan (e.g. Normal, Level II, AQL=1), the chance of accepting a lot can vary considerably (from around 99% down to around 90%, depending on the lot size). Tightening tends to increase the risk of rejecting a good lot but also increases the odds of rejecting a bad lot; reduced sampling tends to reduce the risk of rejecting a good lot, but also increases the odds of accepting a bad lot.

That is one reason I have a couple of times in small ways advoacted getting rid of table-based plans like Z1.4 (or MIL-STD-105, or any of the others) and simply creating a software-based standard where you could specify probabilities instead of such vagaries as Inspection Level and Type. You would instead state someing like "Sample using a plan with alpha = 0.05 for lots with 1% defective, and beta = 5% for lots with 5% defective." You plug it into the computer and it spits out a sample size, an accept number and a reject number.

You could even borrow some of the old language, so that "Normal" might mean
alpha = beta =0.05, AQL would become the % defective associated with alpha, "Level II" would relate to the % defective associated with beta. The only drawback might be that people would actually see how big of risks they are taking :eek: and get scared away from sampling -- then again, maybe thats not a bad thing :cool: !

It just seems in the era when everyone has a computer that could instantly calculate the sampling plan to go with any parameters you could desire, using a printed table is so old-fashioned. But that is just my little soapbox :soap:

Tim F
 
Thread starter Similar threads Forum Replies Date
Y What are different Special Inspection Level 1-4 and General spesification 1-3 ? AQL - Acceptable Quality Level 0
N Visible particles inspection in powders for injections. Approaches to AQL level Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 1
A Level 1 vs. Level 2 vs. Level 3 Inspection Requirements - AS9100 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 1
Q AQL - How do I determine Acceptable Quality Level (AQL) for In-Process Inspection? AQL - Acceptable Quality Level 2
B Customer Inspection Frequency and Rejection Level Criteria - Sample Lot Size AQL - Acceptable Quality Level 6
B Choosing Inspection Level and AQL AQL - Acceptable Quality Level 1
M AQL and the impact of increasing Batch Size, or changing Inspection Level AQL - Acceptable Quality Level 2
H Need help with AQL (Acceptable Quality Level) for a QC inspection AQL - Acceptable Quality Level 8
P Inspection Level Interpretation - ANSI Z1.4-2008 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
N AQL - Sampling plan (variable, inspection level ii, normal inspection S-method) AQL - Acceptable Quality Level 2
S AQL .65 Level III - Take a particular component off 100% Inspection AQL - Acceptable Quality Level 4
T Special Inspection Level 3 (S-3) per ANSI Z 1.4 & its relationship with ISO 2859-1 AQL - Acceptable Quality Level 1
D Confidence Level II or Inspection Level? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
D Difficult Inspection Level/AQL - Verifying it is the correct part AQL - Acceptable Quality Level 5
R Identifying Inspection Level for Critical Components - Medical Devices ISO 13485:2016 - Medical Device Quality Management Systems 5
W How to choose the correct General Inspection Level & AQL level...? AQL - Acceptable Quality Level 5
D What Inspection Level for Small Lot Size and Special Levels (S1-S4)? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 15
T What is AQL, Inspection Level, and Type of Inspection AQL - Acceptable Quality Level 16
J Testing Potential New Hires for a Low Level Part Inspection Position Inspection, Prints (Drawings), Testing, Sampling and Related Topics 5
S Using AQL to get true random sampling using General Inspection Level II AQL - Acceptable Quality Level 4
P Need a programmer for QVI's VMS software for optical inspection machine Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
silentmonkey How to decide what characteristics need to be verified during incoming inspection? ISO 13485:2016 - Medical Device Quality Management Systems 5
J Mechanical inspection techniques of close tolerance parts Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
T Help to Suggest name for a new certification and inspection company Coffee Break and Water Cooler Discussions 7
B GM GP-12 Exit Criteria - Additional Safe Launch Inspection - (Also see GM1927-28 ) Customer and Company Specific Requirements 2
S Process Inspection -Sub assembly process inspection sheet Lean in Manufacturing and Service Industries 3
C OEE and In-process Inspection Manufacturing and Related Processes 2
R AS9100 - 8.4.2 - Receiving Inspection Requirements AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
I Mother bobbin final inspection criteria Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
Marc Visual Inspection - Color Vision Coffee Break and Water Cooler Discussions 15
G Inspection Logs - Asked to remove an Inspection Sheet ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 4
Skooma Receiving Inspection - Boss trying to save money AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 7
T Sample of 1st Article Inspection Report wanted APQP and PPAP 3
T Nonconforming product at customer detected by a routine inspection by field service Nonconformance and Corrective Action 9
A Definition of customer in ITP (Inspection & Test Plan) Contract Review Process 3
T Correct MSA study for an automated camera system which makes attribute inspection Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
A DCMA inspection for a drop-shipment AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
S QUALITY OBJECTIVEs for third party garments factory inspection ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
D Lean and Elimination of QC Inspection Points in a New factory Lean in Manufacturing and Service Industries 9
F FDA-registration and inspection cost 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
I Receiving Inspection Requirement in IATF IATF 16949 - Automotive Quality Systems Standard 3
R Supplier related drawings and verification of process requirements - Source Inspection AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
D AS9100 Inspection records - Is there a requirement to have gauge ID and calibration status AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
D Good Acceptance Activity/Inspection flowchart for reference - Wanted Please Process Maps, Process Mapping and Turtle Diagrams 2
K Inspection Certificate EN 10204 2.1 - Distribution company Other ISO and International Standards and European Regulations 4
S Improving Quality inspection gate in one piece flow manufacturing process Manufacturing and Related Processes 0
M Loss of a Quality Record - FDA Inspection Records and Data - Quality, Legal and Other Evidence 4
S Need Assistance in Visual Inspection - Tiny electronic components AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
S. Moore Is an Annual Layout Inspection the same as an Annual Re-validation? Internal Auditing 1
D Incoming (Receiving) Inspection - General form for incoming part inspection Document Control Systems, Procedures, Forms and Templates 17

Similar threads

Top Bottom