Codex sampling plans for prepackaged foods (aql 5) codex stan 233-1969 scope



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CODEX SAMPLING PLANS FOR PREPACKAGED FOODS (AQL 6.5)

CODEX STAN 233-1969

1. SCOPE

The Sampling Plans in Appendix I of this document apply to the acceptance of defective units (defectives) in lots of prepackaged foods, as defined in individual Codex Standards, insofar as the Sampling Plans have been specifically included in such Codex Standards for the purpose of determining the acceptability or otherwise of the lot. They shall be used in accordance with the provisions dealing with the classification of defectives and lot acceptance in Codex Standards to which these Sampling Plans are stated to apply and within the limits of Section 2 of this document.



2. FIELD OF APPLICATION

2.1. TYPE OF EXAMINATION TO WHICH THE SAMPLING PLANS APPLY

The Sampling Plans in Appendix I of this document are intended primarily to cover the quality provisions of Codex Commodity Standards where an AQL of 6.5 is appropriate for the defective unit as defined in Codex Standards. For the purposes of these Sampling Plans, “quality” refers to those factors or product characteristics which are evaluated by organoleptic or physical means, such as colour, flavour, texture, defects, size and appearance. They are not intended however, to cover factors which may represent a hazard to health or which are unwholesome or otherwise highly objectionable to the consumer on the basis of which responsible authorities would reject the lot. Examples of these latter categories are pesticide residues, contaminants, blown cans, foreign material such as stones and large insects. Other criteria andsampling plans must be used in dealing with factors of this type. While these Sampling Plans are intended primarily for quality evaluation, they may be found suitable for other determinations such as net weight, Brix values and drained weight, provided an acceptance criterion with an AQL of 6.5 is appropriate for these determinations. In this case a definition of “defective” for the specific determination under consideration would be required in the respective Codex Standard.
2.2. SIZE OF LOT AND POINT OF APPLICATION

The Sampling Plans and acceptance procedures contained in this document are designed to cover lots that represent substantial portions of factory production or relatively large blocks of merchandise. The plans may also be used for small lots, but Governments may elect to use sampling procedures of their own choosing for enforcement at the retail level. This is done in recognition of the high ratio of sample size to lot size when dealing with small lots and the probability that once the production of defective or non-conforming product is no longer likely to be uniform between and within the smaller lots.


2.3. PRINCIPLES OF ACCEPTANCE SAMPLING

For detailed explanation of the statistical basis for these Sampling Plans, see Appendix II of this document.


3. DESCRIPTION

The Sampling Plans - Appendix I of this document - are a tabular presentation appropriate for acceptance sampling of prepackaged foods where an AQL of 6.5 has been accepted for certain products characteristics. The Plans include:

1. Inspection Levels;

2. Sample Sizes in relation to lot size and container size; and

3. Acceptance Numbers.

A sample is drawn at random from the lot according to the appropriate schedule in the Sampling Plans. Each sample unit is examined according to the requirements of the individual Codex Standard and classified as either “acceptable” or as “defective”. Based on the total number of “defectives “ in the sample, the lot either “meets” or “fails” the requirements of the Codex standard, to which these Sampling Plans apply, according to the following criteria:

- Meets if the number of “defectives” is equal to, or less than, the acceptance number of the appropriate plan.

- Fails if the number of “defectives” exceeds the acceptance number of the appropriate plan.


4. DEFINITIONS

4.1. ACCEPTABLE QUALITY LEVEL (AQL)

The maximum percent defective units (defectives) permitted in a lot which will be accepted approximately 95 percent of the time. For example, a sampling plan at an AQL of 6.5 will accept a lot or production which has 6.5 percent defective approximately 95 percent of the time.
4.2. ACCEPTANCE NUMBER (C)

The number in a sampling plan which indicates the maximum number of defectives permitted in the sample in order to consider the lot as meeting the requirements of a Codex Standard.

4.3. BUYER’S RISK

The risk a buyer takes that a lot will be accepted on the basis of these Sampling Plans even though such a lot may fail to conform to the requirements of the Codex Standard.



4.4. PRODUCER’S RISK

The risk a producer takes that a lot will fail on the basis of these Sampling Plans even though such a lot in

reality may meet the requirements of the Codex Standard.

4.5. DEFECTIVE

A “defective” is a sample unit which does not conform with a certain specified requirement (or requirements) of a Codex Standard (on the basis of total “demerit points”, individual tolerances for “defects”, etc.). The criteria on the basis of which a sample unit is classified as “defective” are specified in individual Codex standards to which these Sampling Plans apply (see also Sub-sections 2.1 and 2.2 of this document). Although a defective is a sample unit which fails to meet certain specified requirements in Codex standards, it does so only to an extent which is slightly below those requirements and which would not make the product objectionable to the consumer as specified in Section 2 - Field of Application, Sub-section 2.1.



4.6. INSPECTION

The process of measuring, examining, testing or otherwise comparing a container or unit of product (sample unit) with the requirements of a Codex Standard.



4.7. INSPECTION LEVEL

The term used to indicate the relative amount of sampling performed on lots of a given product or class of products.



4.8. LOT OR INSPECTION LOT

Collection of primary containers, or sample units, of the same size, type and style which have been manufactured or processed under essentially the same conditions.



4.9. LOT SIZE (N)

The number of primary containers, or sample units, in the lot.



4.10. SAMPLE UNIT

The individual container (primary container), a portion of the contents of the primary container or a composite mixture of product that is examined or tested as a single unit



4.11. SAMPLE

Any number of sample units which are used for inspection. Generally the sample comprises all of the containers or sample units drawn for examination or testing purposes from a particular lot.



4.12. SAMPLING

The process of drawing or selecting containers or sample units from a lot or production.



4.13. SAMPLE SIZE (N)

The number of containers, or sample units comprising the total sample drawn from a lot or production.




4.14. SAMPLING PLAN

A sampling scheme which includes sample sizes, inspection levels, acceptance and/or rejection numbers so that a decision can be made to accept or reject the lot or production based on the results of inspection and testing of the sample.



5. APPLICATION OF THE SAMPLING PLANS

5.1. INFORMATION REQUIRED

In using the Sampling Plans in Appendix I of this document, the following information shall be known:



  1. ontainer size (net weight in kg or lb)

  2. Inspection Level (see sub-section 4.7)

  3. Lot size (N) (see sub-section 4.9)

  4. Requirements of the Codex Standard with respect to product quality (i.e. classification of defectives and requirements for acceptance of the lot).



5.2. INSPECTION

The following steps are taken:



  1. The appropriate inspection level is selected as follows:

Inspection Level I - Normal sampling

Inspection Level II - Disputes (Codex referee purposes sample size), enforcement or need for better lot estimate.



  1. Determine the lot size (N), i.e. number of primary containers or sample units.

  2. Determine the number of sample units (sample size (n)) to be drawn from the inspection lot, consideration being giving to container size, lot size, and inspection level.

  3. Draw at random the required number of sample units from the lot giving proper consideration to code or other identifying marks in selection of the sample.

  4. Examine the product in accordance with the requirements of the Codex Standard. Classify any container or sample unit which fails to meet the specified quality level of the standard as a defective on the basis of the classification of defectives contained in the Codex Standard.

  5. Refer to the appropriate Sampling Plan in Appendix I.

  6. Consider the lot acceptable if the number of defectives is equal to or is less than the acceptance number (c) of the appropriate Sampling Plan contained in Appendix I of this document.

  7. Consider the lot as failing if the number of defectives exceeds the acceptance number (c) of the appropriate Sampling Plan contained in Appendix I of this document.

5.3. EXAMPLES FOR THE APPLICATION OF THE SAMPLING PLANS

  1. Inspection Level I (see sub-section 5.2 (a))

A lot consists of 1200 cases, packed 12 x 2.5 lb primary containers per case. A decision is made to use inspection Level I since the goods are not in dispute and there is no history of controversy over quality. A container is defined in the Codex Standards or is taken to be the sample unit.

Lot Size (N) = 1200 x 12 or 14,400 units

Container Size = 2.5 lb

Inspection Level = I (see Sampling Plan 1, Appendix I)

Sample size (n) = 13

Acceptance Number (c) = 2

In this example if there are no more than two (2) “defectives” in a sample size of 13 containers the lot is considered acceptable. If, however, there are three (3) or more “defectives” in the sample the lot is considered as failing to meet the requirements. A “defective” as used in the Sampling Plans is defined in the Codex Standard.
b. Inspection Level II (see sub-section 5.2 (a))

If in the foregoing example (5.3 (a)) the quality of the goods is in dispute and a referee method is required for the examination or re-examination of the lot, an increased sample size is taken at Inspection Level II, selecting at least 21 containers.

Lot Size (N) = 1200 x 12 or 14,400 units

Inspection level = II (see Sampling Plan 2, Appendix I)

Sample Size (n) = 21

Acceptance Number (c) = 3



5.4. NOTES ON SAMPLE SIZE

It is not necessary to restrict the sample size to the minimum corresponding to the appropriate lot size and Inspection Level. In all cases a larger sample may be drawn. In the example at 5.3 (b) an even more reliable estimate of lot quality could be made by taking a sample of 29 or even 48 and applying the corresponding acceptance numbers of 4 and 6 respectively.



KÕ ho¹ch lÊy mÉu thùc phÈm ®ãng gãi CODEX

(Møc ChÊt l­îng Cã thÓ chÊp nhËn aql 6,5 )

Tiªu chuÈn CODEX 233-1969


  1. Ph¹m vi

C¸c KÕ ho¹ch LÊy mÉu trong Phô lôc I cña tµi liÖu nµy ¸p dông cho viÖc chÊp nhËn c¸c ®¬n vÞ lçi (lçi) trong thùc phÈm ®ãng gãi, nh­ ®· ®­îc ®Þnh nghÜa trong c¸c Tiªu chuÈn Codex riªng, môc ®Ých KÕ ho¹ch LÊy mÉu trong c¸c Tiªu chuÈn Codex nµy lµ x¸c ®Þnh xem cã thÓ chÊp nhËn l« ®ã hay kh«ng. KÕ ho¹ch LÊy mÉu ph¶i tu©n thñ theo ®iÒu kiÖn ®Ó xÕp lo¹i lçichÊp nhËn l« trong Tiªu chuÈn Codex, mµ ®èi víi Tiªu chuÈn ®ã, nh÷ng KÕ ho¹ch LÊy mÉu nµy míi cã t¸c dông vµ trong ph¹m vi ®­îc nªu trong Môc 2 cña tµi liÖu nµy.



  1. lÜnh vùc ¸p dông

    1. H×nh thøc kiÓm tra cña KÕ ho¹ch lÊy mÉu

Nh÷ng KÕ ho¹ch lÊy mÉu trong Phô lôc 1 cña tµi liÖu nµy cã môc ®Ých chñ yÕu lµ b¶o ®¶m ®iÒu kiÖn vÒ chÊt l­îng cña Tiªu chuÈn Hµng hãa Codex , mµ trong ®ã mét (AQL) 6,5 lµ phï hîp víi sè ®¬n vÞ lçi, nh­ ®· ®­îc ®Þnh nghÜa trong Tiªu chuÈn Codex . §Ó phôc vô cho môc tiªu cña nh÷ng KÕ ho¹ch LÊy mÉu, thuËt ng÷ “chÊt l­îng” ®­îc g¾n víi nh÷ng tiªu chÝ hay ®Æc ®iÓm s¶n phÈm ®­îc ®¸nh gi¸ b»ng ph­¬ng ph¸p c¶m quan hay vËt lý nh­ mµu s¾c, mïi vÞ, kÕt cÊu, khuyÕt tËt, kÝch th­íc, tr¹ng th¸i bªn ngoµi. Dï sao ch¨ng n÷a, nh÷ng KÕ ho¹ch LÊy mÉu kh«ng ®Ò cËp ®Õn c¸c yÕu tè t¹o ra mèi nguy cho søc khoÎ hay cã h¹i cho søc khoÎ hay kh«ng ®­îc kh¸ch hµng chÊp nhËn, mµ c¨n cø vµo ®ã, c¸c c¬ quan chøc n¨ng sÏ lo¹i bá l« ®ã. VÝ dô cho c¸c tr­êng hîp gÇn ®©y lµ d­ l­îng thuèc trõ s©u, chÊt g©y « nhiÔm, ®å hép háng, ngo¹i vËt nh­ ®¸ vµ c«n trïng lín. CÇn sö dông c¸c tiªu chÝ vµ kÕ ho¹ch lÊy mÉu kh¸c ®èi víi nh÷ng yÕu tè lo¹i nµy. MÆc dï nh÷ng KÕ ho¹ch LÊy mÉu nµy cã môc ®Ých chñ yÕu lµ ®¸nh gi¸ chÊt l­îng, nh­ng chóng còng cã thÓ dïng ®Ó ®¸nh gi¸ c¸c yÕu tè kh¸c nh­ träng l­îng tÞnh, chØ sè Brix vµ träng l­îng kh« víi ®iÒu kiÖn tiªu chÝ ph¶i thÝch hîp víi AQL 6,5. Trong tr­êng hîp nµy, ®Þnh nghÜa vÒ “lçi” khi xem xÐt ®¸nh gi¸ cô thÓ nªn ®­îc quy ®Þnh trong mét Tiªu chuÈn Codex riªng.




    1. Quy m« cña l« vµ tr­êng hîp ¸p dông

Nh÷ng KÕ ho¹ch LÊy mÉu vµ thñ tôc c«ng nhËn trong tµi liÖu nµy ®­îc x©y dùng cho c¸c ®¹i diÖn cho nh÷ng s¶n phÈm chÝnh cña nhµ m¸y hay c¸c kiÖn hµng t­¬ng ®èi lín. Còng cã thÓ ¸p dông nh÷ng kÕ ho¹ch nµy cho nh÷ng l« nhá nh­ng mét sè ChÝnh phñ cã thÓ sÏ chän quy tr×nh lÊy mÉu riªng cña hä ®Ó ¸p dông t¹i cÊp b¸n lÎ. ViÖc nµy ®­îc thùc hiÖn trong tr­êng hîp nhËn thÊy tû lÖ quy m« mÉu / quy m« l« cao, th­êng x¶y ra khi xö lý nh÷ng l« hµng nhá vµ kh¶ n¨ng x¶y ra sai lçi cña s¶n phÈm kh«ng cßn mang tÝnh ®ång bé gi÷a c¸c l« hay mang tÝnh ®¹i diÖn tõ mét l« nhá h¬n.




    1. Nguyªn t¾c lÉy mÉu chÊp nhËn

Phô lôc II cña tµi liÖu nµy gi¶i thÝch chi tiÕt vÒ c¬ së thèng kª cña KÕ ho¹ch LÊy mÉu .




  1. M« t¶

KÕ ho¹ch LÊy mÉu (theo Phô lôc I cña tµi liÖu nµy) ®­îc tr×nh bµy d­íi d¹ng b¶ng thÝch hîp cho viÖc lÊy mÉu thùc phÈm ®ãng gãi, mµ t¹i ®ã AQL6,5 lµ chÊp nhËn ®­îc ®èi víi c¸c ®Æc tÝnh cho tr­íc cña s¶n phÈm. KÕ ho¹ch bao gåm:

1. CÊp kiÓm tra

2. Quy m« mÉu t­¬ng øng víi quy m« l« vµ quy m« bao b×; vµ

3. Sè lçi cã thÓ chÊp nhËn

Mét mÉu ®­îc lÊy ngÉu nhiªn tõ mét theo lÞch tr×nh thÝch hîp cña KÕ ho¹ch LÊy mÉu. Mçi ®¬n vÞ mÉu ®­îc kiÓm tra theo yªu cÇu cña tõng Tiªu chuÈn Codex riªng biÖt vµ ®­îc xÕp lo¹i “cã thÓ chÊp nhËn” hoÆc”lçi”. C¨n cø vµo tæng sè “lçi” trong mÉu, KÕ ho¹ch LÊy mÉu sÏ xÕp l« ®ã vµo lo¹i “®¹t” hoÆc “kh«ng ®¹t” tiªu chuÈn Codex , theo c¸c tiªu chÝ sau:



    • §¹t nÕu sè “lçi” b»ng hoÆc thÊp h¬n sè lçi cã thÓ chÊp nhËn cña kÕ ho¹ch t­¬ng øng.

    • Kh«ng ®¹t nÕu sè “lçi” v­ît qu¸ sè lçi cã thÓ chÊp nhËn cña kÕ ho¹ch t­¬ng øng.

  1. §Þnh nghÜa

4.1. Møc ChÊt l­îng Cã thÓ chÊp nhËn (AQL)
§©y lµ sè % tèi ®a c¸c ®¬n vÞ lçi (lçi) cho phÐp cã trong 1 l« sÏ ®óng trong kho¶ng 95% c¸c tr­êng hîp. VÝ dô, mét AQL 6,5 sÏ chÊp nhËn mét l« hay qu¸ tr×nh s¶n xuÊt bÞ lçi 6,5% trong kho¶ng 95% c¸c tr­êng hîp
4.2. Sè chÊp nhËn (C)

Lµ con sè trong mét kÕ ho¹ch lÊy mÉu chØ ra sè lçi tèi ®a ®­îc phÐp cã trong mÉu, mµ theo ®ã cã thÓ xem nh­ l« ®ã ®· ®¹t yªu cÇu cña mét Tiªu chuÈn Codex .

4.3. Mèi nguy ®èi víi ng­êi mua

Lµ mèi nguy mµ ng­êi mua ph¶i g¸nh chÞu khi mµ mét cã thÓ kh«ng ®¸p øng yªu cÇu cña Tiªu chuÈn Codex nh­ng sÏ ®­îc chÊp nhËn dùa trªn nh÷ng KÕ ho¹ch LÊy mÉu nµy.

4.4. Mèi nguy ®èi víi nhµ s¶n xuÊt

Lµ mèi nguy mµ nhµ s¶n xuÊt ph¶i g¸nh chÞu khi mµ mét thùc sù cã thÓ ®¸p øng yªu cÇu cña Tiªu chuÈn Codex nh­ng l¹i kh«ng ®­îc chÊp nhËn dùa trªn nh÷ng KÕ ho¹ch LÊy mÉu nµy.

4.5. Lçi

Mét “lçi” lµ mét ®¬n vÞ mÉu kh«ng tu©n theo mét hay nhiÒu yªu cÇu cô thÓ nhÊt ®Þnh cña mét Tiªu chuÈn Codex (dùa vµo tæng sè “khuyÕt ®iÓm”, c¸c dung sai riªng ®èi víi “khuyÕt tËt”…). Tiªu chÝ ®Ó xÕp lo¹i ®¬n vÞ mÉu bÞ coi lµ “lçi” ®­îc quy ®Þnh cô thÓ trong c¸c Tiªu chuÈn Codex riªng, mµ ®èi víi Tiªu chuÈn ®ã nh÷ng KÕ ho¹ch lÊy mÉu nµy míi cã t¸c dông (xem môc 2.1 vµ 2.2 cña tµi liÖu nµy). MÆc dï mét lçi lµ mét ®¬n vÞ mÉu kh«ng ®¸p øng yªu cÇu cô thÓ nhÊt ®Þnh trong Tiªu chuÈn Codex, nh­ng trong mét chõng mùc nµo ®ã, nã chØ h¬i thÊp h¬n yªu cÇu vµ kh«ng ®Õn møc lµm cho s¶n phÈm bÞ kh¸ch hµng tõ chèi nh­ ®· nªu trong Môc 2 - Ph¹m vi ¸p dông - môc 2.1


4.6. KiÓm tra

Lµ qu¸ tr×nh ®o l­êng, thÈm tra, kiÓm nghiÖm hoÆc c¸c ph­¬ng ph¸p kh¸c ®Ó so s¸nh mét hép hay mét ®¬n vÞ s¶n phÈm (®¬n vÞ mÉu) víi c¸c yªu cÇu cña mét Tiªu chuÈn Codex.



4.7. CÊp kiÓm tra
Lµ thuËt ng÷ dïng ®Ó chØ sè l­îng lÊy mÉu t­¬ng øng tõ c¸c cña 1 s¶n phÈm hay d·y s¶n phÈm cho tr­íc.

4.8. L« hay l« kiÓm tra

Lµ tËp hîp c¸c hép nguyªn hay c¸c ®¬n vÞ mÉu cïng kÝch th­íc, chñng lo¹i, kiÓu d¸ng ®­îc s¶n xuÊt hay chÕ biÕn trong c¸c ®iÒu kiÖn t­¬ng ®ång.



4.9. Quy m« cña L« (N)

Lµ sè hép nguyªn hay sè ®¬n vÞ mÉu cã trong .



4.10. §¬n vÞ mÉu

Lµ mét hép riªng biÖt (hép nguyªn), mét phÇn trong thµnh phÇn cña hép nguyªn hoÆc mét hçn hîp s¶n phÈm ®­îc kiÓm tra hoÆc kiÓm nghiÖm nh­ mét ®¬n vÞ ®éc lËp.



4.11. MÉu

Lµ bÊt kú sè ®¬n vÞ mÉu nµo ®­îc sö dông ®Ó kiÓm tra. Nh×n chung mÉu bao gåm tÊt c¶ c¸c hép hoÆc c¸c ®¬n vÞ mÉu, ®­îc lÊy ra tõ mét cô thÓ ®Ó kiÓm tra hoÆc kiÓm nghiÖm.



4.12. LÊy mÉu

Lµ c«ng ®o¹n lÊy hoÆc lùa chän hép hoÆc ®¬n vÞ mÉu tõ mét l« hay mét qu¸ tr×nh s¶n xuÊt.



4.13. Quy m« mÉu (N)

Lµ sè hép hay ®¬n vÞ mÉu bao gåm tæng sè mÉu lÊy tõ mét hay mét qu¸ tr×nh s¶n xuÊt.


4.14. KÕ ho¹ch LÊy mÉu

Lµ mét lÞch tr×nh lÊy mÉu bao gåm quy m« mÉubËc kiÓm tra, sè lçi cã thÓ chÊp nhËn vµ/hoÆc kh«ng thÓ chÊp nhËn, ®Ó tõ ®ã ®­a ra quyÕt ®Þnh chÊp nhËn hay kh«ng chÊp nhËn hay qu¸ tr×nh s¶n xuÊt dùa trªn kÕt qu¶ kiÓm tra vµ kiÓm nghiÖm mÉu.



5. ¸p dông KÕ ho¹ch lÊy mÉu

5.1. Th«ng tin cÇn thiÕt

§Ó sö dông KÕ ho¹ch LÊy mÉu trong Phô lôc I cña tµi liÖu nµy, cÇn ph¶i biÕt nh÷ng th«ng tin sau:

a. Quy m« hép (träng l­îng tÞnh - kg hoÆc pound)

b. CÊp kiÓm tra (xem môc 4.7)

c. Quy m« cña l« (N) (xem môc 4.9)

d. C¸c yªu cÇu cña Tiªu chuÈn Codex vÒ chÊt l­îng s¶n phÈm (cã nghÜa lµ ph©n lo¹i lçi vµ c¸c ®iÒu kiÖn ®Ó chÊp nhËn l« s¶n phÈm)



5.2. KiÓm tra

C¸c b­íc tiÕn hµnh nh­ sau:

a. Lùa chän cÊp kiÓm tra thÝch hîp d­íi ®©y:

KiÓm tra cÊp I - LÊy mÉu th«ng th­êng

KiÓm tra cÊp II - Tranh chÊp (träng tµi Codex quyÕt ®Þnh quy m« mÉu), b¾t buéc hoÆc cÇn thiÕt ®Ó ®¸nh gi¸ l« tèt h¬n.

b. X¸c ®Þnh quy m« l« (N), nghÜa lµ sè hép nguyªn hay ®¬n vÞ mÉu.

c. X¸c ®Þnh sè ®¬n vÞ mÉu (quy m« mÉu (n)) sÏ lÊy tõ l« kiÓm tra dùa trªn quy m« hép, quy m« l«cÊp kiÓm tra.

d. LÊy ngÉu nhiªn ®ñ sè ®¬n vÞ mÉu theo yªu cÇu tõ cã xem xÐt thÝch hîp vÒ m· sè hay c¸c dÊu hiÖu nhËn d¹ng kh¸c khi chän mÉu.

e. KiÓm tra s¶n phÈm theo yªu cÇu cña Tiªu chuÈn Codex. XÕp bÊt cø hép hay ®¬n vÞ mÉu nµo kh«ng ®¹t møc chÊt l­îng vµo lo¹i bÞ lçi dùa trªn sù xÕp lo¹i lçi trong Tiªu chuÈn Codex.

f. Tham chiÕu KÕ ho¹ch LÊy mÉu thÝch hîp trong Phô lôc I

g. KÕt luËn l« cã thÓ chÊp nhËn nÕu sè lçi b»ng hoÆc thÊp h¬n sè lçi cã thÓ chÊp nhËn (c) cña KÕ ho¹ch LÊy mÉu trong Phô lôc I cña tµi liÖu nµy.

h. KÕt luËn kh«ng ®¹t nÕu sè lçi v­ît qu¸ sè lçi cã thÓ chÊp nhËn theo KÕ ho¹ch LÊy mÉu trong Phô lôc I cña tµi liÖu nµy.



5.3. VÝ dô vÒ ¸p dông KÕ ho¹ch lÊy mÉu

a. KiÓm tra cÊp I (xem môc 5.2 (a))

Mét s¶n phÈm cã 1200 thïng, mçi thïng cã 12 hép nÆng 2,5 pound. QuyÕt ®Þnh ¸p dông KiÓm tra cÊp I v× kh«ng cã tranh chÊp hay cã tiÒn sö tranh c·i vÒ chÊt l­îng hµng. Hép ®ùng s¶n phÈm, theo ®Þnh nghÜa trong Tiªu chuÈn Codex, hay mét hép bÊt kú ®­îc lÊy ra tõ l« gäi lµ mét ®¬n vÞ mÉu.

Quy m« l« s¶n phÈm (N) = 1200 x 12 hay 14.400 hép (®¬n vÞ)

Quy m« hép = 2,5 pound

CÊp kiÓm tra = I (xem KÕ ho¹ch lÊy mÉu 1,Phô lôc I)

Quy m« mÉu (n) = 13

Sè hép bÞ lçi cã thÓ chÊp nhËn = 2

Trong vÝ dô nµy, nÕu sè hép bÞ lçi kh«ng nhiÒu h¬n hai (2) trong mét quy m« mÉu cã 13 hép th× hµng ®­îc coi lµ cã thÓ chÊp nhËn. Tuy nhiªn, nÕu sè lçi trong mÉu tõ ba (3) trë lªn, hµng bÞ coi lµ kh«ng ®¹t tiªu chuÈn. Kh¸i niÖm “lçi” sö dông trong KÕ ho¹ch LÊy mÉu ®­îc ®Þnh nghÜa trong Tiªu chuÈn Codex.



KiÓm tra cÊp II (xem môc 5.2 (a))

NÕu trong vÝ dô trªn (5.3 (a)), cã tranh chÊp vÒ chÊt l­îng hµng vµ ph­¬ng ph¸p träng tµi ®­îc yªu cÇu ®Ó kiÓm tra hay t¸i kiÓm tra th× ¸p dông KiÓm tra cÊp II vµ cÇn quy m« mÉu lín h¬n, Ýt nhÊt lµ 21 hép.

Quy m« l« s¶n phÈm (N) = 1200 x 12 hay 14.400 ®¬n vÞ

CÊp kiÓm tra = II (xem KÕ ho¹ch lÊy mÉu 2,Phô lôc I)

Quy m« mÉu (n) = 21

Sè lçi cã thÓ chÊp nhËn (c) = 3



5.4. L­u ý vÒ quy m« mÉu

Kh«ng nhÊt thiÕt ph¶i h¹n chÕ quy m« mÉu xuèng møc tèi thiÓu t­¬ng øng víi quy m« l«CÊp kiÓm tra. Trong mäi tr­êng hîp, ®Òu cã thÓ lÊy mÉu nhiÒu h¬n, vÝ dô ë môc 5.3 (b), cã thÓ ®¸nh gi¸ chÊt l­îng b»ng c¸ch lÊy mÉu víi quy m« lµ 29 hép hay thËm chÝ 48 hép vµ ¸p dông sè lçi cã thÓ chÊp nhËn t­¬ng øng lµ 4 hoÆc 6.

.



Phô lôc I

APPENDIX I


KÕ ho¹ch lÊy mÉu 1

(KiÓm tra cÊp I, AQL = 6,5)

Khèi l­îng tÞnh b»ng hoÆc thÊp h¬n 1 kg (2,2 pound)

SAMPLING PLAN 1

(Inspection Level I, AQL = 6.5)

NET WEIGHT IS EQUAL TO OR LESS THAN 1 KG ( 2.2LB)


Quy m« l« (N)

Lot Size (N)



Quy m« mÉu (n)

Sample Size (n)



Sè lçi cã thÓ chÊp nhËn (c)

Acceptance Number (c)



 4.800

6

1

4,801 - 24.000

13

2

24.001 - 48.000

21

3

48.001 - 84.000

29

4

84.001 - 144.000

38

5

144.001 - 240.000

48

6

 240.000

60

7


Khèi l­îng tÞnh trªn 1 kg (2,2 pound) nh­ng kh«ng qu¸ 4,5 kg (10 pound)

NET WEIGHT IS GREATER THAN 1 KG (2.2LB) BUT NOT MORE THAN 4.5 KG (10LB)


Quy m« l« (N)

Lot Size (N)



Quy m« mÉu (n)

Sample Size (n)



Sè lçi cã thÓ chÊp nhËn (c)

Acceptance Number (c)



 2.400

6

1

2.401 - 15.000

13

2

15.001 - 24.000

21

3

24.001 - 42.000

29

4

42.001 - 72.000

38

5

72.001 - 120.000

48

6

 120.000

60

7



Khèi l­îng tÞnh trªn 4.5 kg (10 pound)

NET WEIGHT GREATER THAN 4.5 KG (10 LB)


Quy m« l« (N)

Lot Size (N)



Quy m« mÉu (n)

Sample Size (n)



Sè lçi cã thÓ chÊp nhËn (c)

Acceptance Number (c)



 600

6

1

601 - 2.000

13

2

2.001 - 7.200

21

3

7.201 - 15.000

29

4

15.001 - 24.000

38

5

24.001 - 42.000

48

6

 42.000

60

7


KÕ ho¹ch lÊy mÉu 2

(KiÓm tra cÊp II, AQL = 6,5)

Khèi l­îng tÞnh b»ng hoÆc thÊp h¬n 1 kg (2,2 pound)

SAMPLING PLAN 2

(Inspection Level II, AQL = 6.5)

NET WEIGHT IS EQUAL TO OR LESS THAN 1 KG (2.2 LB)


Quy m« l« (N)

Lot Size (N)



Quy m« mÉu (n)

Sample Size (n)



Sè lçi cã thÓ chÊp nhËn (c)

Acceptance Number (c)



 4.800

13

2

4,801 - 24.000

21

3

24.001 - 48.000

29

4

48.001 - 84.000

38

5

84.001 - 144.000

48

6

144.001 - 240.000

60

7

 240.000

72

8



Khèi l­îng tÞnh trªn 1 kg (2,2 pound) nh­ng kh«ng qu¸ 4,5 kg (10 pound)

NET WEGHT IS GREATER THAN 1 KG (2.2 LB) BUT NOT MORE THAN 4.5 KG (10 LB)


Quy m« l« s¶n phÈm (N)

Lot Size (N)



Quy m« mÉu (n)

Sample Size (n)



Sè lçi cã thÓ chÊp nhËn (c)

Acceptance Number (c)



 2.400

13

2

2.401 - 15.000

21

3

15.001 - 24.000

29

4

24.001 - 42.000

38

5

42.001 - 72.000

48

6

72.001 - 120.000

60

7

 120.000

72

8



Khèi l­îng tÞnh trªn 4.5 kg (10 pound)

NET WEIGHT GREATER THAN 4.5 KG (10 LB)


Quy m« l« s¶n phÈm (N)

Lot Size (N)



Quy m« mÉu (n)

Sample Size (n)



Sè lçi cã thÓ chÊp nhËn (c)

Acceptance Number (c)



 600

13

2

601 - 2.000

21

3

2.001 - 7.200

29

4

7.201 - 15.000

38

5

15.001 - 24.000

48

6

24.001 - 42.000

60

7

 42.000

72

8



APPENDIX II

EXPLANATORY NOTES ON ACCEPTANCE SAMPLING


SAMPLING

Sampling is the process of drawing or selecting containers or sample units from a lot or production. As a result of sampling, information is obtained by which an estimate can be made to accept, reject or negotiate the merchandise in question. Sampling procedures which contain both sample size and acceptance criteria are commonly referred to as “acceptance sampling”.

There are many types of acceptance sampling systems in use today. A plan that is suitable for one product or type of inspection may be entirely unsuitable for another product or inspection system. The plan selected is determined to a large extent by the degree to which it satifies the needs of the user.

In developing these acceptance sampling plans, initial consideration has been given to quality evaluation of the end product. This requires opening of containers with resultant loss of products. This type of inspection is referred to as “destructive sampling”. Not only is the loss of product an important consideration, but also destructive sampling is generally quite time consuming, Consequently, both inspection time and economic loss of product through destructive inspection are significant limiting factors in developing sampling plans for quality evaluation of processed foods. Sample size must necessarily be relatively small in order to make the plan practical in application.



RISKS

The aim of any sampling plan should be to accept more “good” lots and reject more “bad”lots. Since probability and chance are involved, decisions will, of necessity, involve an element of risk. This risk factor has to be accepted as a part of any sampling procedure. One method of reducing the buyer’s risk of accepting deliveries of non-conforming quality is to increase sample size. In other words, the larger the sample, the less risk involved in accepting “bad” lots. Inspection level is the term indicating the relative amount of sampling and inspection performed on lots of a given product or class of products. If the inspection lot is packed under close control and meets the requirements of the Codex Standard, changing inspection levels do not appreciably change the buyer-seller risk. In other words, this would be a “good” lot and should be passed practically all of the time by a good sampling plan. The effectiveness of a sampling plan in discriminating between “good” and “bad” lots can be estimated by examination of the OC curves (see Appendix III) for the various sample sizes. For example, if a lot is produced so that it does not contain more than 6.5 percent defectives, such lot will be passed at least 95 percent of the time by the sampling plans applicable for an AQL of 6.5. On the other hand, if the production contains an appreciable amount of defective material, a higher inspection level (i.e. a larger sample size) will reduce the risk of accepting these non-conforming lots. The effect of increased sample size is explained in greater detail under the discussion of OC curves.




AQL

One of the initial considerations in the development of a statistical acceptance sampling plan is the selection of an appropriate AQL or Acceptable Quality Level. This characteristic is defined as the maximum percent defective units in lots that will be accepted most of the time (approximately 95 percent of the time). Lots or production containing more defective material will be accepted less often - the ratio of rejection to acceptance increasing as the sample size increases and as the percent defective material in the lot increases.

In developing these sampling plans, an AQL of 6.5 was selected for lot acceptance with respect to quality evaluation. In other words, an AQL of 6.5 is used in these sampling plans (Appendix I) to determine whether or not the inspection lot meets minimum quality requirements of the Codex Standard. This value was selected on the basis of years of experience and the capability of industry to produce preserved fruits and vegetables and certain other processed foods at this level under good commercial practice. For other factors (such as Brix value and net weight) other AQLs may be selected. Sampling plans can be drawn up for a full range of AQLs from a very strict value of 0.10 to a rather lenient value of 25.0 and higher,

depending either on the type of product and/or on the criteria involved.



INSPECTION LEVEL

These sampling plans provide for two inspection levels, I and II. These two levels provide some discretion in the application of the Sampling Plans to the inspection of a commodity, depending upon circumstances. For normal trading purposes Level I is recommended. In the case of dispute or controversy, i.e. for Codex referee purposes, Level II is recommended. Smaller sample sizes than those provided by Levels I and II may be justified, e.g. when a delivery is being checked for labelling or for detection of non-permitted additives. However, the acceptance sampling criteria of the Plans, which permit 6.5 percent “defectives”, do not apply to such an inspection.


OC CURVES

The problem of buyer’s and seller’s risks in relation to sample size and lot quality is illustrated through the use of Operating Characteristic Curves (OC Curves). Appendix III contains OC Curves for the sampling plans contained in Appendix I of this document. For Purposes of destructive inspection sample sizes in excess of 84 are not practical, since any further inspection beyond this point will not generally provide sufficient additional data to warrant the time and expense of testing.

In studying the OC Curves for AQL 6.5 several conclusions can be drawn, namely:


    1. All of the Curves have the same general slope although the curve for sample size 6 is flatter.

    2. All curves intersect at a point represented by the coordinates of “6.5 percent defective”and approximately “95 percent probability of acceptance”.

    3. As the sample size increases, the curves become steeper and more discriminating, i.e. lots having “defectives” in excess of 6.5 percent are rejected with greater frequency.

    4. The reliability of the larger sample size is not in direct proportion to the increased sample. For example, for a lot that is 20 percent defective a sample size of 6 (curve E) will accept such lot 65 percent of the time; whereas a sample size of 48 (curve L) will accept the same lot 22 percent of the time. In this example the ratio between probabilities of acceptance is only 3 to 1.

To illustrate the use of the OC Curves (AQL 6.5) let it be assumed that a lot is 10 percent defective. A lot

with 6.5 percent defectives will be accepted approximately 95 percent of the time, the frequency of

acceptance increasing as the percent defective decreases. However, the 10 percent defective lot fails to measure up to requirements, and while it may be a marginal lot, it may not be acceptable. An examination

of the OC curves shows that a sample size of 6 (curve E) will accept this marginal lot 88 percent of the

time; a sample size of 84 (curve M) is somewhat better, accepting the lot 65 percent of the time.

If, on the other hand, the lot is 30 percent defective, a sample size of 6 (curve E) will accept the lot only 42

percent of the time, whereas a sample size of 21 (curve J) will accept such a lot only 8 percent of the time and a sample size of 84 (curve M) will always fail such a lot.


Phô lôc II

Chó gi¶i vÒ lÊy mÉu chÊp nhËn

LÊy mÉu

LÊy mÉu lµ c«ng ®o¹n lÊy hay chän hép ®ùng s¶n phÈm hoÆc ®¬n vÞ mÉu tõ mét l« hay mét qu¸ tr×nh s¶n xuÊt. LÊy mÉu cung cÊp nh÷ng th«ng tin mµ dùa vµo ®ã ng­êi ta cã thÓ ®¸nh gi¸ nh»m chÊp nhËn, tõ chèi hay th­¬ng th¶o l« hµng cã vÊn ®Ò. Thñ tôc lÊy mÉu bao gåm c¶ quy m« mÉu vµ c¸c tiªu chÝ chÊp nhËn th­êng ®­îc gäi lµ “lÊy mÉu chÊp nhËn”.

Cã nhiÒu kiÓu hÖ thèng lÊy mÉu chÊp nhËn hiÖn hµnh. Mét kÕ ho¹ch cã thÓ phï hîp víi mét s¶n phÈm hay mét h×nh thøc kiÓm tra nµy nh­ng l¹i cã thÓ kh«ng hoµn toµn phï hîp víi mét s¶n phÈm hay hÖ thèng kiÓm tra kh¸c. Ph¹m vi cña kÕ ho¹ch ®­îc x¸c ®Þnh nh»m tho¶ m·n c¸c yªu cÇu cña ng­êi sö dông.

Khi x©y dùng nh÷ng kÕ ho¹ch lÊy mÉu chÊp nhËn nµy, yÕu tè ®Çu tiªn cÇn xem xÐt lµ ®¸nh gi¸ chÊt l­îng thµnh phÈm. ViÖc nµy ®ßi hái ph¶i më hép dÉn ®Õn viÖc tiªu hao s¶n phÈm. H×nh thøc kiÓm tra nµy gäi lµ “ lÊy mÉu cã tÝnh ph¸ ho¹i”. VÊn ®Ò ë ®©y lµ c¸ch lÊy mÉu nµy kh«ng chØ lµm tiªu hao s¶n phÈm mµ cßn g©y mÊt thêi gian. KÕt qu¶ lµ thêi gian kiÓm tra vµ thiÖt h¹i kinh tÕ do ph­¬ng ph¸p nµy g©y ra lµ nh÷ng yÕu tè mang tÝnh h¹n chÕ quan träng khi tiÕn hµnh x©y dùng KÕ ho¹ch lÊy mÉu ®¸nh gi¸ chÊt l­îng thùc phÈm chÕ biÕn. Quy m« mÉu cÇn ph¶i t­¬ng ®èi nhá ®Ó kÕ ho¹ch cã tÝnh thùc tÕ khi ¸p dông.



Mèi nguy

Môc tiªu cña mäi kÕ ho¹ch lÊy mÉu lµ chÊp nhËn nhiÒu h¬n c¸c l« hµng tèt vµ lo¹i bá nhiÒu h¬n c¸c l« hµng xÊu. Do dung sai vµ c¬ may lµ nh÷ng yÕu tè kh«ng tr¸nh khái, v× vËy, vÒ c¬ b¶n c¸c quyÕt ®Þnh th­êng bao hµm c¶ mèi nguy. YÕu tè mèi nguy ph¶i ®­îc chÊp nhËn vµ coi nh­ mét phÇn cña mäi thñ tôc lÊy mÉu. Mét ph­¬ng ph¸p nh»m gi¶m mèi nguy cho ng­êi mua khi nhËn ®­îc c¸c s¶n phÈm kh«ng ®¹t yªu cÇu chÊt l­îng lµ t¨ng quy m« mÉu. Nãi c¸ch kh¸c, quy m« mÉu cµng lín, mèi nguy cã liªn quan ®Õn viÖc chÊp nhËn c¸c l« hµng xÊu cµng gi¶m. CÊp kiÓm tra lµ thuËt ng÷ dïng ®Ó chØ sè l­îng lÊy mÉu vµ kiÓm tra t­¬ng øng ®èi víi c¸c l« hµng cña mét s¶n phÈm hay líp s¶n phÈm cho tr­íc. NÕu l« kiÓm tra ®­îc kiÓm so¸t chÆt chÏ vµ ®¸p øng c¸c yªu cÇu trong Tiªu chuÈn Codex th× viÖc thay ®æi cÊp kiÓm tra kh«ng lµm thay ®æi ®¸ng kÓ mèi nguy cña bªn mua vµ bªn b¸n. NghÜa lµ, ®©y sÏ lµ mét l« hµng tèt vµ trong mäi tr­êng hîp trªn thùc tÕ ®­îc th«ng qua bëi mét KÕ ho¹ch lÊy mÉu tèt. HiÖu qu¶ cña mét KÕ ho¹ch lÊy mÉu trong viÖc ph©n biÖt c¸c l« hµng “tèt” vµ “xÊu” cã thÓ ®­îc ®¸nh gi¸ nhê viÖc xem xÐt c¸c ®­êng trong ®å thÞ m« t¶ quy tr×nh (xem phô lôc III) ®èi víi mét sè quy m« mÉu kh¸c nhau. VÝ dô, nÕu mét l« s¶n phÈm ®­îc s¶n xuÊt cã møc lçi kh«ng cao h¬n 6.5, l« s¶n phÈm ®ã sÏ ®­îc nh÷ng KÕ ho¹ch lÊy mÉu víi AQL= 6,5 th«ng qua trong Ýt nhÊt 95% c¸c tr­êng hîp. NÕu qu¸ tr×nh s¶n xuÊt cã sè lçi ®¸ng kÓ, sö dông mét cÊp kiÓm tra cao h¬n (quy m« mÉu lín h¬n) sÏ gi¶m nguy c¬ cña viÖc chÊp nhËn c¸c l« hµng kh«ng ®¹t nµy. HiÖu qu¶ cña viÖc t¨ng quy m« mÉu ®­îc tr×nh bµy kü h¬n trong phÇn c¸c ®­êng ®å thÞ m« t¶ quy tr×nh.



AQL

Mét trong nh÷ng viÖc cÇn xem xÐt hµng ®Çu khi x©y dùng mét KÕ ho¹ch lÊy mÉu lµ lùa chän Møc ChÊt l­îng Cã thÓ chÊp nhËn (AQL) thÝch hîp. Kh¸i niÖm nµy ®­îc ®Þnh nghÜa lµ sè % tèi ®a c¸c ®¬n vÞ lçi (lçi) ®­îc phÐp trong 1 l« sÏ ®­îc chÊp nhËn trong hÇu hÕt c¸c tr­êng hîp (kho¶ng 95%). C¸c l« hay qu¸ tr×nh s¶n xuÊt cã nhiÒu lçi h¬n sÏ Ýt ®­îc chÊp nhËn h¬n- tû lÖ gi÷a kh«ng chÊp nhËn vµ chÊp nhËn t¨ng khi quy m« mÉu t¨ng vµ khi sè lçi cña l« t¨ng.

Khi x©y dùng nh÷ng KÕ ho¹ch lÊy mÉu nµy, AQL= 6,5 ®­îc chän ®Ó chÊp nhËn l« hµng khi ®¸nh gi¸ chÊt l­îng. Nãi c¸ch kh¸c, AQL 6,5 ®­îc ¸p dông cho nh÷ng KÕ ho¹ch lÊy mÉu trong phô lôc I ®Ó x¸c ®Þnh liÖu l« hµng ®­îc kiÓm tra cã ®¸p øng c¸c yªu cÇu tèi thiÓu vÒ chÊt l­îng cña Tiªu chuÈn Codex hay kh«ng. Gi¸ trÞ nµy ®­îc rót ra tõ nhiÒu n¨m kinh nghiÖm vµ n¨ng lùc cña nghµnh c«ng nghiÖp s¶n xuÊt rau qu¶ ®­îc b¶o qu¶n vµ mét sè thùc phÈm chÕ biÕn nhÊt ®Þnh t¹i møc nµy trong t×nh h×nh th­¬ng m¹i thuËn lîi. §èi víi c¸c yÕu tè kh¸c nh­ gi¸ trÞ Brix vµ khèi l­îng tÞnh, cã thÓ ¸p dông c¸c AQL kh¸c. Cã thÓ x©y dùng KÕ ho¹ch lÊy mÉu víi mét lo¹t c¸c AQL víi møc thÊp nh­ 0,10 vµ cao nh­ 25,0 vµ thËm chÝ cßn cao h¬n n÷a c¨n cø vµo lo¹i s¶n phÈm vµ/hoÆc tiªu chÝ cã liªn quan.
CÊp kiÓm tra

Cã 2 cÊp kiÓm tra trong KÕ ho¹ch lÊy mÉu, cÊp I vµ II. Hai cÊp kiÓm tra nµy cho phÐp lùa chän c¸ch ¸p dông KÕ ho¹ch LÊy mÉu ®Ó kiÓm tra hµng ho¸ tuú thuéc vµo hoµn c¶nh cô thÓ. KiÓm tra cÊp I nªn ¸p dông ®èi víi nh÷ng môc ®Ých th­êng m¹i th«ng th­êng. Trong tr­êng hîp cã tranh chÊp hay tranh c·i, nghÜa lµ cÇn cã träng tµi Codex, nªn ¸p dông cÊp kiÓm tra II. Ngoµi ra, cã thÓ ¸p dông c¸c quy m« mÉu nhá h¬n quy m« ë cÊp I, II trong mét sè tr­êng hîp, vÝ dô nh­ kiÓm tra vÒ ghi nh·n l« hµng hay dß t×m c¸c phô gia kh«ng ®­îc phÐp. Tuy nhiªn, c¸c tiªu chÝ chÊp nhËn mÉu cña KÕ ho¹ch cho phÐp møc lçi 6,5% kh«ng hiÖu qu¶ ®èi víi h×nh thøc kiÓm tra nµy.


§­êng ®å thÞ cong OC

VÊn ®Ò mèi nguy ®èi víi ng­êi mua vµ ng­êi b¸n liªn quan ®Õn quy m« mÉu vµ chÊt l­îng l« hµng ®­îc minh ho¹ b»ng c¸c §­êng §Æc tÝnh Ho¹t ®éng (§­êng cong OC). Phô lôc III bao gåm c¸c ®­êng cong m« t¶ c¸c KÕ ho¹ch LÊy mÉu trong Phô lôc I cña tµi liÖu nµy. §èi víi viÖc kiÓm tra cã tÝnh ph¸ ho¹i, quy m« mÉu trªn 84 lµ kh«ng thùc tÕ v× mäi ho¹t ®éng kiÓm tra s©u h¬n v­ît qu¸ møc nµy sÏ kh«ng cung cÊp ®ñ sè liÖu bæ sung ®¶m b¶o vÒ thêi gian vµ chi phÝ kiÓm tra.

Nghiªn cøu c¸c ®­êng ®å thÞ m« t¶ quy tr×nh víi AQL 6,5 cã thÓ ®i ®Õn nh÷ng kÕt luËn sau:

1. TÊt c¶ c¸c ®­êng cong nãi chung cã cïng ®é dèc, tuy nhiªn ®­êng cong cña quy m« mÉu 6 b»ng ph¼ng h¬n.

2. TÊt c¶ c¸c ®­êng cong gÆp nhau t¹i mét ®iÓm ë to¹ ®é gi÷a “møc lçi 6,5%” vµ kho¶ng “95% kh¶ n¨ng chÊp nhËn”.

3. Khi quy m« mÉu t¨ng, c¸c ®­êng cong dèc h¬n vµ t¸ch biÖt h¬n, nghÜa lµ c¸c l« cã møc lçi v­ît qu¸ 6,5 bÞ tõ chèi th­êng xuyªn h¬n.


4. §é tin cËy cña quy m« mÉu lín h¬n kh«ng t­¬ng quan trùc tiÕp víi sè mÉu t¨ng lªn. VÝ dô, víi l« cã møc lçi 20%, quy m« mÉu 6 (®­êng cong E) sÏ chØ chÊp nhËn l« hµng trong 65% c¸c tr­êng hîp; trong khi ®ã quy m« mÉu 48 (®­êng cong L) chØ chÊp nhËn l« hµng trong 22% c¸c tr­êng hîp. Trong vÝ dô trªn, tû lÖ gi÷a c¸c kh¶ n¨ng chÊp nhËn chØ lµ 3/1.

§Ó minh ho¹ cho viÖc sö dông c¸c §õ¬ng OC (AQL= 6,5), cÇn gi¶ ®Þnh r»ng l« cã møc lçi 10%. L« cã møc lçi 6,5% ®­îc chÊp nhËn trong 95% c¸c tr­êng hîp, nh­ vËy, tÇn sè ®­îc chÊp nhËn t¨ng khi sè % lçi gi¶m. L« trªn cã lçi 10% nªn kh«ng ®¹t yªu cÇu, khi ®ã nã lµ l« n»m ë ngoµi lÒ vµ nã sÏ kh«ng ®­îc chÊp nhËn. Xem xÐt c¸c ®­êng ®å thÞ m« t¶ quy tr×nh cho thÊy quy m« mÉu 6 (®­êng cong E) sÏ chÊp nhËn l« ngoµi lÒ nµy trong 88% c¸c tr­êng hîp; quy m« mÉu 84 (®­êng cong M) cã phÇn kh¸ h¬n khi chÊp nhËn l« nµy trong 65% c¸c tr­êng hîp.



MÆt kh¸c, nÕu l« cã lçi 30%, quy m« mÉu 6 (®­êng cong E) chØ chÊp nhËn l« hµng trong 42% c¸c tr­êng hîp trong khi quy m« mÉu 21 (®­êng cong J) chØ chÊp nhËn l« nµy trong 8% c¸c tr­êng hîp vµ quy m« mÉu 84 (®­êng cong M) lu«n kh«ng chÊp nhËn l« nµy.









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