acceptance sampling 2

In manufacturing of Tablets

If every tablet was tested for hardness, no tablet

would be left for sale. If, on other hand, none of tablets were tested

for hardness, malfunctions might occur, which

may lead to variation in results for

Dissolution test and

Disintegration test.

A Seminar on

ACCEPTANCE SAMPLING

Presented By

Mr. Mohit G. Dewani

(M. Pharm, Quality Assurance, II Semester)

Under the Guidance of

Mrs. Mrinalini C. Damle

23rd April 2009

AISSMS College of Pharmacy, Pune-01

CONTENTS

Introduction When is accepting sampling employed? Sampling risks The O.C. Curve Quality indexes for sampling plans Types of Sampling Types of Sampling plans ANSI/ASQC Z1.4 Example

3AISSMS College of Pharmacy, Pune 01

CONTENTS (contd…)

Rules for switching inspection severity Dodge-Romig sampling plans Acceptance sampling – Method Reduces sampling costs with acceptance sampling Moving from 100% inspection to 0% sampling. Acceptance sampling standards

1) Military standards

2) International standards organization (ISO)

3) American national standards institute (ANSI) References


INTRODUCTION

• Acceptance sampling is the process of evaluating a small sample of the product in a given lot for purpose of accepting or rejecting a lot, based on the conformance or non-conformance of the sample to quality specifications.

• The main purpose of acceptance sampling is to decide whether or not lot is acceptable,

not to estimate the quality of the lot.


When is acceptance sampling employed?

1) Testing is destructive.

2) The Cost of 100 % inspection is very high.

3) 100 % inspection takes too long.

Acceptance sampling is the “middle of the road” approach between no inspection and

100 % inspection.


• Acceptance sampling can be applied at any point in production.

• The output of one stage is the input of the next.


• Sampling plans decide which lots of product to accept and release and which lots to reject and either rework or discard.

• Ideally, a sampling plan should reject all "bad" lots while accepting all "good" lots.

• However, because the sampling plan bases it decision on a sample of the lot and not the entire lot, there is always a chance of making an incorrect decision.

• The behavior of a sampling plan is described by the sampling plan's Operating Characteristic (OC) curve.


SAMPLING RISKS


SAMPLING RISKS

AISSMS College of Pharmacy, Pune 01 10

The Operating Characteristic (O.C.) Curve


Quality Indexes for Sampling Plans

1) Acceptable quality level (AQL)

2) Limiting quality level (LQL)

3) Indifference quality level (IQL)

4) Average outgoing quality limit (AOQL)



1. Acceptable quality level (AQL) –• The AQL is a percent defective that is the base

line requirement for the quality of the producer's product.

• The producer would like to design a sampling plan such that there is a high probability of accepting a lot that has a defect level less than or equal to the AQL.



2. Limiting quality level (LQL) –• LQL defines unsatisfactory quality.

• Also called Lot tolerance percentage defective (LTPD).

• The probability of acceptance of LQL should be low.

3. Indifference quality level (IQL) –• It is somewhere between AQL and LQL.

• The probability of acceptance of IQL is 0.5 for a given

sampling plan.



4. Average outgoing quality level (AOQL) –• When incoming quality is perfect, outgoing quality must

also be perfect.

• However, when incoming quality is bad, (assuming no inspection errors) outgoing quality will also be perfect, because the sampling plan will cause all lots to be rejected and inspected in detail.

• Thus at either extreme – incoming quality excellent or terrible – the outgoing quality will tend to be good.


Types of Sampling


Types of Sampling plans

1) Attributes plans (“go no-go”) A random sample is taken from the lot, and each unit is

classified as acceptable or defective. The number defective is then compared with the

allowable number stated in the plan, and a decision is made to accept or reject the lot.


Types of Sampling plans

2) Variables plans (continuous) A sample is taken, and measurement of a specified

quality characteristic is made on each unit. These measurements are then summarized into a sample

statistic. (e.g., sample average), and the observed value is then compared with the allowable value defined in the plan.

A decision is made to accept or reject the lot.


Types of Sampling Plans

1) Single Sampling

2) Double Sampling

3) Multiple Sampling

4) Sequential Sampling

5) Skip – Lot Sampling

6) Random Sampling

7) Stratified Sampling

8) Sampling Bias

9) Bulk Sampling


SINGLE SAMPLING


DOUBLE SAMPLING

AISSMS College of Pharmacy, Pune 01

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MULTIPLE SAMPLING

• This is an extension of the double sampling plans where more than two samples are needed to reach a conclusion.

• The advantage of multiple sampling is smaller sample sizes.


SEQUENTIAL SAMPLING


SEQUENTIAL SAMPLING

Also called “item-by-item” sequential sampling. If the plotted point falls within the parallel lines the process

continues by drawing another sample. If a point falls on or above the upper line, the lot is

rejected. And when a point falls on or below the lower line, the lot is accepted. The process can theoretically last until the lot is 100% inspected.

However, as a rule of thumb, sequential-sampling plans are truncated after the number inspected reaches three times the number that would have been inspected using a corresponding single sampling plan


SKIP – LOT SAMPLING

Skip Lot sampling means that only a fraction of the submitted lots are inspected.

This mode of sampling is of the cost-saving variety in terms of time and effort.

However skip-lot sampling should only be used when it has been demonstrated that the quality of the submitted product is very good.


RANDOM SAMPLING

Samples are drawn at random, i.e., at any one time each of the remaining uninspected units of the product has an equal chance of being the next unit selected for sample.

E.g., for fluid or well-mixed bulk products, the fluidity obivates the need for random numbers, and the samples may be taken from “here and there”.


STRATIFIED SAMPLING

When the “lots” are known to come from different machines, production shifts, operators, etc, the product is actually multiple lots which have been arbitrarily combined.

In such cases, an attempt is made to draw the sample proportionately from each true lot.


SAMPLING BIAS

Sampling from same location in all containers, racks or bins.

Previewing the product and selecting only those units which appear to be defective.


BULK SAMPLING

Bulk materials may be of gaseous, liquid or solid form. Usually it is sampled by taking increments into a single composite sample and then, if necessary, reducing this gross sample to a size suitable for laboratory testing.


ANSI/ASQC Z1.4 (1993)

• ANSI/ASQC Z1.4 is an attribute sampling system.

• ANSI (American National Standards Institute)

• ASQC (American Society of Quality Control)

• Its quality index is AQL.


Suppose in a lot of 1500 pieces, purchasing agency has contracted for a 1.5% AQL.

1) What should be the sample size?

2) From the corresponding sample size, what will be the acceptance number and rejection number?

3) Explain the single, double and multiple plans

for the corresponding sample size.

4) What will be the switching procedure or

tightened plan for the above sample size?

NOTE: To solve the above problem, refer charts provided.


Dodge – Romig sampling plans

• These plans differ from those in ANSI/AQC Z1.4 in that the Dodge-Romig plans (1959) assume that all rejected lots are 100% inspected and the defectives are replaced with acceptable items.

• Plans with this feature are also called rectifying inspection plans.

• It provides four sets of attribute plans:

1) LTPD – single sampling & double sampling

2) AOQL - single sampling & double sampling


Acceptance sampling: Method


Reduce inspection costs with acceptance sampling

Generate sampling plan as an alternative to 100% inspection.

E.g; you plan to randomly sample 96 light bulbs from the shipment. If you find two or fewer defective bulbs, you will accept the entire lot of bulbs. Otherwise, the entire lot of bulbs will be rejected.

Sample size – 96

Acceptance number - 2


Interpretation made from the above O.C. curve.

By sharing this OC curve with your supervisor, you can point out that the resulting consumer risk is much too high for you to consider reducing your sample size to 50.

The OC curve can also be shown to your supplier to prove that the resulting consumer risk is much too high for you to consider raising your acceptance number to 10.

Perhaps you will evaluate other

acceptance numbers between 2 and 10.


ACCEPTANCE SAMPLING STANDARDS


Sr. No.

Military Standards Guidance

1 MIL-STD-1916 (1996) Preferred Methods for Acceptance of Product

2 MIL-HDBK-1916 (1999) Companion Document to MIL-STD-1916

3 MIL-STD-105E (1989) Sampling Procedures and Tables for Inspection by Attributes

4 MIL-STD-414 (1968) Sampling Procedures and Tables for Inspection by Variables for Percent Nonconforming

5 MIL-STD-1235C (1974) Single and Multi-Level Continuous Sampling Procedures and Tables for Inspection by Attributes

6 MIL-HDBK-781A (1 April 1996)

Handbook for Reliability Test Methods, Plans, and Environments for Engineering, Development Qualification, and Production


Sr. No.

International Standards

Organization (ISO)

Guidance

1 ISO 2859-0:1995 Sampling procedures for inspection by attributes – Part 0 : Introduction to the ISO 2859 attribute sampling system

2 ISO 2859-1:1999 Sampling procedures for inspection by attributes -- Part 1 :Sampling plans indexed by acceptable quality level (AQL) for lot-by-lot inspection

3 ISO 2859-2:1985 Sampling procedures for inspection by attributes -- Part 2: Sampling plans indexed by limiting quality (LQ) for isolated lot inspection

4 ISO 7966:1993 Acceptance control charts



Sr. No.

ANSI Guidance

1 ANSI/ASQC Z1.4-2008 Sampling Procedures and Tables for Inspection by Attributes

2 ANSI/ASQC Z1.9-2008 Sampling Procedures and Tables for Inspection by Variables for Percent Nonconforming

3 ANSI/ASQC Q3-1988 Sampling Procedures and Tables for Inspection of Isolated Lots by Attributes

4 ANSI/ASQC S1-1987 (R1995)

An Attribute Skip-Lot Sampling Program

5 ANSI/ASQC S2-1995 Introduction to Attribute Sampling

6 ANSI/EIA 584-1991 Zero Acceptance Number Sampling Procedures and Tables for Inspection by Attributes of a Continuous Manufacturing Process

44

REFERENCES

1) J. M. Juran, F. M. Gryna; Juran’s Quality Control Handbook; Fourth edition; Mc Graw-Hill book company, New York; PP. 25.1-25.103.

2) F. M. Gryna, R. C. H. Chua, J. A. Defeo; Juran’s Quality planning and analysis for enterprise quality (2009); Fifth edition; Tata Mc-Graw Hill publishing company ltd., New Delhi; PP. 496-513.

3) Y. Anjaneyulu, R. Marayya; Quality assurance and quality management in pharmaceutical industry (2005); Pharma book syndicate, Hyderabad; P. 174.


REFERENCES

4) S. W. Bergman, J. C. Gittins; Statistical methods for pharmaceutical research planning; vol. 67; Marcel Dekker Inc., New York; PP. 110,129,132.

5) http://www.itl.nist.gov/div898/handbook/pmc/section2/pmc21.htm (accessed on - 13th April 2010).

6) http://www.itl.nist.gov/div898/handbook/pmc/section2/pmc22.htm (accessed on - 14th April 2010).

7) http://www.mintab.com/uploadedFiles/Shared_Resources/Documents/Articles/Acceptance_Sampling.pdf (accessed on - 14th April 2010)


REFERENCES

8)http://www.cimt.plymouth.ac.uk/projects/mepres/alevel/fstats_ch9.pdf (accessed on - 15th April 2010).

9) http://www.itl.nist.gov/div898/handbook/pmc/section2/

pmc2.htm (accessed on - 17th April 2010).

10) luisdi.files.wordpress.com/2009/08/quality-as.pdf (accessed on - 20th April 2010).

11) www.ansi.org (accessed on – 21st April 2010)


Any Questions???


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