LESSON 2 Statistical Sampling

LESSON 2 Statistical Sampling
15November2013

Lesson Introduction Given a surveillance requirement, the student will be able to apply statistical sampling techniques to supplier contract activities.

Lesson Objectives Upon completion of this lesson, you should be able to: Relate the importance of sampling to Quality Assurance (QA) surveillance responsibilities. Distinguish between Inspection by Attributes and Inspection by Variables. Distinguish between the three types of inspection: Normal, Reduced, and Tightened. Outline the internal Defense Contract Management Agency (DCMA) process of Zero-based sampling. Use randomization tools to generate random numbers for a simple random sample. Lesson 4: Safety Stock

Lesson Objectives (cont.)
Upon completion of this lesson, you should be able to: Differentiate between simple, systematic, cluster, and stratified sampling techniques. Interpret information presented on Zero-based sampling system tables. Interpret information presented on American National Standards Institute (ANSI)/American Society for Quality (ASQ) Z sampling system tables. Interpret information presented on Military Standard (MIL- STD)-1916 sampling system tables. Determine whether to initiate acceptance or non-acceptance activities based on sampling results. Lesson 4: Safety Stock

Lesson Topics This lesson will cover the following topics:
Importance of Sampling to QA Inspection by Attribute vs. Inspection by Variable Three types of Inspection Under a Sampling Plan Zero-Based Sampling Generating Random Sample Numbers Simple, Systematic, Cluster, and Stratified Sampling Techniques Interpreting Zero-Based Sampling System Tables Interpreting ANSI/ASQZ Sampling System Tables Interpreting MIL-STD-1916 Sampling System Tables Initiating Acceptance and Non acceptance Activities

WIIFM? This lesson is important because:
Zero-Based sampling is a tool used to ensure suppliers present and the Quality Assurance Specialist (QAS) accepts conforming product DCMA policy to use Zero-based sampling Random sampling techniques Statistically valid sampling plan Multiple sampling plans exist, including: ANSI/ASQ Z MIL-STD 1916

DCMA Policy Use Zero-Based Sampling Use random sampling techniques
Use statistically valid sampling plans Ensure supplier: Meets contractual requirements Understands and uses statistically valid sampling plans If product examination is determined the appropriate surveillance method, the QAS should verify supplier’s conformance by sampling.

Sampling Terms (1 of 4) Sampling System Sampling Scheme Sampling
Sampling System - collection of sampling schemes indexed by lot-size ranges, inspection levels, and Acceptable Quality Levels (AQLs) (i.e., ANSI/ASQ Z ) DCMA Policy: The QAS will use zero-based sampling unless otherwise stated in a QALI. Sampling System Sampling Scheme Sampling Scheme Sample Plan 1 Sample Plan 1 Sample Plan 2 Sample Plan 2 Sample Plan 3 Sample Plan 3 Sample Plan 4 Sample Plan 4

Sampling Terms (2 of 4) Sampling Scheme
Sampling Scheme - combination of sampling plans with switching rules and provision for discontinuance of inspection (i.e., Normal, Reduced, or Tightened) Individual Sampling Plan - plan stating sample size(s) and acceptance criteria (i.e., AQL) Sampling Scheme Sample Plan 1 Sample Plan 2 Sample Plan 3 Sample Plan 4

Sampling Terms (3 of 4) Attribute - a characteristic or property appraised in terms of whether it does or does not exist, (e.g., go or no go) with respect to a given requirement Characteristic - a physical, chemical, visual, functional, or any other identifiable property of a product, material, or unit identified by the product specification, standard, drawing, etc. Defect - a departure of a quality characteristic from its intended level or state that occurs with a severity sufficient to cause an associated product or service not to satisfy intended normal, or foreseeable, usage requirements (ANSI/ASQ Z ) Nonconformity - a departure of a quality characteristic from its intended level or state that occurs with a severity sufficient to cause an associated product or service not to meet a specification requirement; a unit of product that contains one or more defects (ANSI/ASQ Z )

Sampling Terms (4 of 4) Lot or Batch - shall mean “inspection lot” or “inspection batch,” i.e., a collection of units of product from which a sample is drawn and inspected to determine conformance with the acceptability criteria, and may differ from a collection of units designated as a lot or batch for other purposes (e.g., production, shipment, etc.) (ANSI/ASQ Z ) Lot or Batch Size - the number of units of product in a lot or batch Homogeneity - manufactured under essentially the same conditions and essentially at the same time

Acceptable Quality Level (AQL)
Acceptable Quality Level (AQL) - the quality level that is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling. Process Average - the average percent of nonconforming or average number of nonconformities per hundred units (whichever is applicable) of product submitted by the supplier for original inspection. Percent Nonconforming = Number Nonconforming X 100 Number of Units Inspected Nonconformities per Hundred Units X Number Nonconformities 100 Number of Units Inspected Note: One or more nonconformities being possible in any unit

Importance of Sampling to QA
Lesson Topics: Importance of Sampling to QA Inspection by Attribute vs. Inspection by Variable Three Types of Inspection Under a Sampling Plan Zero-Based Sampling Generating Random Sample Numbers Simple, Systematic, Cluster, and Stratified Sampling Techniques Interpreting Zero-Based Sampling System Tables Interpreting ANSI/ASQZ Sampling System Tables Interpreting MIL-STD-1916 Sampling System Tables Initiating Acceptance and Non Acceptance Activities

Topic1: Importance of Sampling to QA
Mr. Shields: Statistical Sampling Importance

What is Sampling? The term, “Sample,” refers to a portion of a population that is representative of the population from which it was selected. The sample is a subset of the population. Population Sample

What is Acceptance Sampling?
Acceptance sampling is selecting and inspecting only a representative smaller subset (sample) selected from a larger lot or batch (population), for the purpose of making an accept/reject decision of an entire lot or batch based on the inspection results of the sample only. Acceptance sampling is used by suppliers and DCMA to validate product quality.

Accurate Assessment of the Population
Why Should We Sample? Accurate Assessment of the Population Saves Time Cost Effective Why Sampling 100% Not Always Possible Customer Requests

Random Sampling Mr. Shields: Random Sampling Example

What is Random Sampling?
Product Random Sample The term Random Sampling refers to a sampling procedure where every unit in the population has an equal chance of being selected as part of the sample The objective of the sampling procedure is to ensure that the final samples to be measured or tested are representative of the population from which they were taken ILLUSTRATE random sampling procedure Every item in that population has an equal opportunity to be selected If the sample taken is not representative of the population, then it is a biased sample, which can lead to misleading results. Random sample can be drawn in several ways: When material is packaged or laid out on a bench in groups or rows, each unit may be numbered from 1 to the total and a sample selected using a random number table For bulk material a numbered area or zone can be used to lay the material out. Samples can be drawn from numbered zones located by using a random number generator. ASK the question: What is your answer if a contractor comes to you and says, “We are almost done with this lot, only one more skid to go. Can you go ahead and take your sample from this?” DISCUSS answer: No, because every item has not had the equal opportunity to be selected in the sample.

Zero-Based Sampling Plans
Lot is accepted when zero defects are discovered Lot is not accepted when one defect is discovered These type plans are also referred to as: Acceptance equals 0 (C=0) Zero-Based Acceptance (ZBA) Accept on Zero (AoZ) During product examination Use statistically valid sampling systems Measure product characteristics Ensure compliance with manufacturing specification requirements

Sampling Risks Customer’s Risk Producer’s Risk Acceptance of Nonconforming Product Non-Acceptance of Conforming Product Because the “lot” disposition is based on sample results, there is a probability of making an incorrect disposition concerning “lot” acceptance.

Inspection by Attribute vs. Inspection by Variable

Topic 2: Inspection by Attribute vs. Inspection by Variable
GO NO GO Attribute Variable 23

Inspection by Attributes
Inspection, whereby either the unit of product is classified simply as conforming or nonconforming, or the number of nonconformities in the unit of products is counted, with respect to a given requirement or set of requirements (ANSI/ASQ Z ) Documentation examples include: Good/Bad Pass/Fail Yes/No Go/No go

Inspection by Variables
Inspection wherein certain quality characteristics of sample are evaluated with respect to a continuous numerical scale and expressed as precise points along this scale. Variables inspection identifies the degree of conformance or nonconformance of the characteristic to the specified requirements. Documentation examples include: Dimension Weight Pressure

Three types of inspection under a sampling plan

Topic 3: Three Types of Inspection Under a Sampling Plan
Normal Inspection Reduced Inspection Tightened Inspection

Types of Inspection Normal Inspection Reduced Inspection
Inspection under a sampling plan that is used when there is no evidence that the quality of the product being submitted is better or poorer than the specified quality level (ANSI/ASQ Z ) Reduced Inspection Inspection under a sampling plan using the same quality level as normal inspection, but requiring a smaller sample for inspection (ANSI/ASQ Z ) Tightened Inspection Inspection under a sampling plan using the same quality level as normal inspection, but requiring more stringent acceptance criteria

Zero-based Sampling Lesson Topics: Importance of Sampling to QA
Inspection by Attribute vs. Inspection by Variable Three Types of Inspection Under a Sampling Plan Zero-Based Sampling Generating Random Sample Numbers Simple, Systematic, Cluster, and Stratified Sampling Techniques Interpreting Zero-Based Sampling System Tables Interpreting ANSI/ASQZ Sampling System Tables Interpreting MIL-STD-1916 Sampling System Tables Initiating Acceptance and Non Acceptance Activities

Topic 4: Zero-Based Sampling
Process overview includes making determinations of: Population Criteria Method Sample size Execute Decisions

Zero-Based Sampling Process Overview
Population Define the population to be examined Criteria Identify inspection/acceptance criteria Method Determine the sample system and size Sample Determine the random-sampling technique Execute Perform the examination and document results Decisions Initiate acceptance or non-acceptance actions

Zero-Based Sampling Process Details
Population Define the population to be examined Contractual products or services To be provided by contract requirement Population may represent Product during manufacturing or in-process product examination Product final acceptance Presented after supplier has determined product quality After supplier’s inspection or test May be divided into subsets Units by machine/units, by shift/units, by day/units, by customer

Criteria Identify inspection/acceptance criteria Identify and document the product characteristics or specification requirements to be examined by sampling Determine the product acceptance criteria for each: Product characteristic to be examined Specification requirement to be validated The product characteristics, features, or specification requirements elected must be present and examinable in/on every product unit in the population and sample

Zero-Based Sampling Process Details (1 of 3)
Method Determine the sample system and size Determine contractual (supplier) sampling requirement: ANSI/ASQ Z /MIL-STD-1916/Government approved plan Use zero acceptance number sampling plans (Squeglia) Unless directed by the customer [Quality Assurance Letter of Instruction (QALI)] Use contract or DCMA criteria for determining AQL Select sample size per the sampling system tables Identify accept/reject number from system tables Zero-Based (C=0) when not contractually mandated

Method Determine the sample system and size (cont.) Samples are selected independent of supplier's sample When AQL is not specified in contract or QALI: AQL=0.4 - All critical characteristics on CSI AQL=1.0 – Complex/critical products and/or CSI significant characteristics AQL=4.0 – Non-complex/non-critical product Sample size is determined by the AQL and lot size

Method Determine the sample system and size (cont.) Sample selection is dependent on lot formation Identified by product serial number, production number, some other form of identification Identified by shift, by machine, by operator, by model, by customer designation Product unit identification Allows for randomization using tables of random numbers Random sampling shall be used even without unit identification or traceability

Zero-based Sampling Plan: AQL Chart

Zero-based Sampling Plan: Example

Product Examination Sheet Sampler Tab
Product Examination Sheet also contains an automated Zero-Based AQL chart that identifies sample size. Product Examination Sheet

Question and Answer What is the sample size if the lot size is 285 and it is a critical characteristic for the product which is a critical safety item? 125 48 29 11 Select the graphic to view the chart.

Question and Answer What is the sample size if the lot size is 35,000 and the product is a non-complex item? 60 315 108 29 Select the graphic to view the chart.

Random Sampling Process Details
Sample Determine the sampling technique Common techniques include: Simple random sampling Systematic sampling Cluster sampling Stratified sampling The sampling technique will always be random Randomization is DCMA policy The use of a random number generator is preferred The use of Microsoft Excel random number generator is easy Method used should be documented in surveillance plan

The Product Examination Policy page includes a project for Helpful QA Tools and provides: 1711 Random Generator tool Random Generator 5 (Excel© spreadsheet) (for other random generators)

Generating Random Sample Numbers

Topic 5: Generating Random Sample Numbers
Microsoft Excel Random Generator Random.org

Random Sampling Process Details
Sample Simple random sampling technique Simple random sampling is a sample in which every member of the population has an equal chance of being selected Small sample sizes Use Microsoft Excel© Random Generator (preferred) Other forms of random sampling based on probability Larger samples sizes Use Microsoft Excel© Random Number Generator

Using Excel to Generate Random Numbers
Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

Determine a way to individualize the product unit for sampling purposes. This could be a serial number, supplier identified number, or other unique number used to ID or track the unit. Use the copy and paste function to import information from the supplier’s documentation. Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

Enter the random number generator formula =RAND() into the cells adjacent to the serial number used. Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

Use the mouse to highlight both rows of cells containing the serial numbers (in this example) and the random numbers. Highlighting keeps column A and B together as a pair. Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

After highlighting columns A and B, select the Sort icon and sort on the column containing the random numbers (in the example, it is B). Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

Notice that the list of serial numbers has also been sorted to correspond with the random number sort. The product units have been randomly sorted. Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

Using Simple Random Sampling techniques, this is the sample of 13 product units to be examined. Randomization Example Zero Acceptance Number Sampling Plan C = 0 AQL = 1.0 Lot Size = 25 Sample Size = 13

Using Random.Org Random Number Generator

Practice Practice using to obtain a random sample. Lot size of 1200. Sample size of 34.

Simple, Systematic, Cluster, and Stratified Sampling Techniques

Topic 6: Simple, Systematic, Cluster, and Stratified Sampling Techniques
Four Sampling Techniques Simple Systematic Cluster Stratified

Zero-Based Sampling Process Details: Simple
Sample Simple random sampling technique Simple random sampling is a sampling from an entire population It is highly representative if each member of the population has an equal chance of being selected Requires complete list of population numbers

Zero-Based Sampling Process Details: Systematic
Sample Systematic sampling technique In systematic sampling, every Kth member of the population is chosen for the sample, with the value of K being approximately: Random number generator can be used to determine starting point (unit) of pulling the sample Results in less time and money spent N (size of population) n+1 (n = sample size) = K

Zero-Based Sampling Process Details: Systematic (cont.)
Sample Systematic sampling technique, example Example: 700 units in population with 34 as the sample size N (size of population) n+1 (n = sample size) = K 700 = 20 35

Zero-Based Sampling Process Details: Cluster
Sample Cluster sampling technique A cluster sample is a simple random sample of groups or clusters, of the population Each unit of the chosen clusters would be part of the final sample To be effective, it is assumed that each cluster selected for the sample is representative of the population at large A cluster is a miniaturized version of the overall population

Zero-Based Sampling Process Details: Cluster (cont.)
Sample Size Cluster sampling technique, example 40K Gloves (population) 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 10 Crates (clusters) containing 4000 gloves each Sample size = 3 10 10 9 Total of 29 samples

Zero-Based Sampling Process Details: Stratified
Sample Stratified sampling technique A stratified sample is obtained by dividing the population into mutually exclusive groups or strata, and randomly sampling from each of these groups Independent samples are randomly selected from each strata Each strata is sampled as an independent sub-population

Zero-Based Sampling Process Details: Stratified (cont.)
Sample Stratified sampling technique example 40K Gloves (population) Strata 20K 10K 10K L M S 29 22 Sample Size The entire lot (40K) must be homogeneous/like products produced under similar conditions

Question and Answer Using the cluster sampling technique, how many crates would be selected from which to pull your samples? Example: 5000 population, 10 crates of 500 each, AQL of .40 13 10 8 3 Select the graphic to view the chart.

Question and Answer How many samples are required to represent the entire population? Example: 5000 population, 10 clusters of 500 each, AQL of 1.0 130 100 50 13 Select the graphic to view the chart.

Interpreting Zero-based Sampling System Tables

Topic 7: Interpreting Zero-based Sampling System Tables
When using zero-based sampling, use the AQL chart to determine sample size.

Zero-Based Sampling Plan, AQL Chart

Operating Characteristic Curve Chart

Tabulated Values for Operating Characteristic Curves for Single Sampling Plans
Two risks associated with sampling. Producers risk – the risk of rejecting product with satisfactory quality. Consumer risk – the risk of accepting product of unsatisfactory quality.

Interpreting MIL-STD-1916 Sampling System Tables

Topic 8: Interpreting ANSI/ASQZ1.4-2008 Sampling System Tables
ANSI/ASQZ Sampling is another sampling plan used in some contracts.

ANSI/ASQZ1.4-2008 Sampling System Table Interpretation
ANSI/ASQZ is a sampling specification often specified in contractual documents that: Is considered the replacement of MIL-STD-105E Is not Zero-Based Contains sampling schemes which include sampling plans Contains switching rules that are dependent upon previous lot inspection/test results Remember: Even though these sampling plans have other accept/reject quantities in them, DCMA uses Accept on Zero/Reject on one unless otherwise directed by the customer.

ANSI/ASQZ1.4-2008 Sampling System
Example: This is the first time a complex part is being offered for acceptance, and there is a lot size of 100 units. Find the code letter for this lot under “General Inspection Levels II”

ANSI/ASQZ1.4-2008: Choose Sampling Plan Type
Since this is the first time the supplier is offering this complex part for acceptance, which sampling plan (normal, tightened, or reduced) should be used? START NORMAL (Reference Switching Rules for ANSI Z1.4 System)

ANSI/ASQZ1.4-2008: Choose AQL
Which AQL should be used?

ANSI/ASQZ1.4-2008: Number of Samples Required

ANSI/ASQZ1.4-2008: Number of Samples Required (cont.)
The supplier has now produced 10 consecutive lots of this part without nonconformities and its production is steady. The supplier switches to reduced sampling level. How many samples are required?

Switching Rules Preceding 10 lots accepted Total nonconforming less than limit number (optional) Production steady Approved by responsible authority START 2 of 5 or fewer consecutive lots are not accepted REDUCED NORMAL TIGHTENED Lot not accepted Lot accepted but nonconformities found lie between Ac and Re of plan Production irregular Other conditions warrant 5 consecutive lots accepted 5 lots not accepted while on Tightened inspection When switching from normal to tightened or reduced inspection, the sample size changes but not the AQL. Discontinue inspection under Z1.4

ANSI/ASQZ1.4-2008: Choose Sampling Plan Type
The supplier had been doing so well that the Government increased the orders from the supplier. To keep up with demand, the supplier had to purchase another milling machine. Now the last three lots have had defects. The supplier was using Reduced sampling, which sampling plan should the supplier be using now? 2 defective lots REJECT REDUCED 1 defective lot REJECT NORMAL TIGHTENED

ANSI/ASQZ1.4-2008: Number of Samples Required (cont.)
How many samples will be required for Tightened; Lot of 100?

Exercise: ANSI-ASQ Z1.4 Sampling Example
Students read the scenario and use the associated tables to determine answers. Open CMQ101_M4_L2_E1_ANSI_ASQ.pdf file. Answer questions on the following screens using the polling device. Time: 15 minutes

Question and Answer The initial lot is ready to inspect. What is the sample size? 50 125 315 All

Question and Answer Ten (10) consecutive lots have been found conforming. According to switching rules, what is the sample size? 50 80 125 200

Question and Answer After being at reduced inspection, 3 lots have been found nonconforming. According to switching rules, what is the sample size? 315 200 125 80

Interpreting MIL-STD-1916 Sampling System Tables

Topic 9: Interpreting MIL-STD-1916 Sampling System Tables
Contains three sampling plans: Attributes Variables Continuous Separates intensity of sampling into Verification Levels (VL) based upon criticality of product characteristics Normal, Reduced, and Tightened switching rules are the same as ANSI/ASQ Z 2 defective lots

MIL-STD-1916: Sample Size What sample size would be used for a 5000 pc lot at Verification Level IV? Step 1:

MIL-STD-1916: Sample Size (cont.)
What sample size would be used for a 5000 pc lot at Verification Level IV? Step 2:

MIL-STD-1916: Nonconformities Solution
If this lot and the next lot both contain nonconformities, what must the supplier do, according to MIL-STD-1916? Initiate Corrective Action and Tighten Sampling

MIL-STD-1916: Sample Size for Tightened Plan
Still using the D code letter, what would the sample size be for a pc lot, specified as Verification Level IV, using Tightened Inspection? EXPLAIN how to obtain sampling size for tightened inspection: Sample code letter is still D (click to show) Specified verification level is 4 (click to display) Must switch to tightened sampling (click to display note) To switch to tightened, shift up one verification level to 5 (click to shift up to V and show new sample size) New sample size is 384 POINT OUT that to shift to tightened, move one verification level to the left of normal. Reduced would be one level to the right of normal.

Exercise: MIL-STD-1916 Sampling Example
Students read the scenario and use the associated tables to determine answers. Open CMQ101_M4_L2_E2_MIL_STD.pdf file. Answer questions on the following screens using the polling device. Time: 15 minutes

Question and Answer The initial lot is ready to inspect. What is the sample size? 48 128 320 All

Question and Answer Ten (10) consecutive lots have been found conforming. According to switching rules, what is the sample size? 48 80 96 320

Question and Answer After being at reduced inspection, 3 of the last 5 lots are found nonconforming. According to switching rules, what is the sample size? 48 128 320 All

Initiating Acceptance and Non acceptance Activities

Topic 10: Initiating Acceptance and Non acceptance Activities
Execute Perform sampling Document results Decisions Acceptance Non-acceptance

Sampling Process Details (1 of 4)
Execute Perform the sampling and document results Perform examination of the product characteristics, features, or specification requirements as identified in the GCQA surveillance plan Accept/reject number from sampling system tables Zero-Based (C=0) - accept on 0 defects, reject on 1 defect Document the results of the examinations in accordance with agency policy requirements Adjust risk assessment based on results Update GCQA surveillance plan accordingly

Decisions Initiate acceptance or non-acceptance actions Notify the supplier of the results Accept/non-accept decision Verify supplier’s compliance with: Lot rejection Requirements concerning lot screening Defect investigation Product replacement Corrective action

Decisions Initiate acceptance or non-acceptance actions (cont.) When using Zero-Based sampling, the entire lot is rejected when one (1) defect is found in the sample The supplier shall tender to the Government for acceptance only supplies that have been inspected in accordance with the inspection system and have been found by the supplier to be in conformity with contract requirements… The supplier shall remove supplies rejected or required to be corrected. Adjust sampling levels as provided for in sampling system or policy

Decisions Initiate acceptance or non-acceptance actions (cont.) Initiated inspection levels will start at normal Unless specified in the sampling system Switching rules As specified in the sampling system If not specified Tightened Inspection 2 Lots nonconforming out of 5 or less Normal 1 Lot nonconforming 5 consecutive conforming Lots Reduced 10 consecutive conforming Lots Switching increases or reduces sample size, not quality standards

Summary (1 of 3) Having completed this lesson, you should now understand: Sampling is important to ensure acceptance of conforming product. Two types of inspection: Attribute and Variable Three levels of inspection: normal, reduced, and tightened. DCMA process for sampling must be used. Use of a random number generator preferred; DCMA QA policy includes links to random number generator tools. DCMA policy mandates zero-based sampling unless otherwise specified by the customer. Lesson 4: Safety Stock

Summary (2 of 3) Having completed this lesson, you should now understand: Sampling techniques: Simple Systematic Cluster Stratified Zero-based sampling system tables: CSI critical characteristics use AQL of 0.40% Complex/critical products or DCMA identified significant characteristics use AQL of 1.0% Non-complex/non-critical products use AQL of 4.0% Lesson 4: Safety Stock

Summary (3 of 3) Having completed this lesson, you should now understand: ANSI/ASQ Z sampling system tables: General inspection levels II is the starting point unless otherwise specified Separate AQL tables for normal, reduced, and tightened Switching rules apply Military Standard (MIL-STD)-1916 sampling system tables: Includes 3 sampling plans for attributes, variables and continuous Verification levels instead of AQLs Same switching rules as ANSI/ASQ Z When using zero-based sampling, entire lot is rejected when one defect is found. Lesson 4: Safety Stock

Questions

Review Question 1 Which is NOT a reason to sample?
100% inspection is not possible Saves time and money Each product must be inspected Customer requests it

Review Question 2 What type of sampling plan is required by DCMA policy? Simple Zero-based ANSI/ASQ Z MIL-STD 1916

Review Question 3 What AQL is required for a Critical Safety Item (CSI) critical characteristic? .040% 0.40% 4.0% 1.0%

Review Question 4 What sampling technique requires a complete list of population numbers? Simple Systematic Cluster Stratified

Review Question 5 What is an appropriate technique when sampling large quantities presented in numerous crates? Simple Systematic Cluster Stratified

Review Question 6 Which technique uses the equation displayed here?
N (size of population) n+1 (n = sample size) = K Simple Systematic Cluster Stratified

Review Question 7 Inspection level for initial inspection starts at _________. Normal Reduced Tightened Variable

Review Question 8 At normal inspection with 2 nonconforming lots, what is the next step? Continue at normal inspection level; notify supplier Switch to reduced inspection level; initiate corrective action Initiate corrective action; switch to tightened inspection level Switch to tightened inspection level for 1 lot; back to normal

Review Question 9 After 10 consecutive conforming lots at normal inspection, switch to _____________. Normal Reduced Tightened Variable

Review Question 10 When changing from Normal to Reduced or Tightened inspection, the QAS is _______________. Changing the AQL Changing the lot size Changing the population size Changing the sample size

Review Question 11 When is a lot rejected if using the Zero-based plan? 0 defects 1 defect 2 non critical defects 2 defects

Exercise: Sampling Plan
Students work in pairs to answer the questions in the exercise. Open CMQ101_M4_L2_E3_SamplingPlan.pdf file.

LESSON 2 Statistical Sampling

Similar presentations

Presentation on theme: "LESSON 2 Statistical Sampling"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

LESSON 2 Statistical Sampling

Similar presentations

Presentation on theme: "LESSON 2 Statistical Sampling"— Presentation transcript:

Similar presentations

About project

Feedback