sampling lot in final audit

7/30/2019 Sampling Lot in Final Audit

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Sampling lot in final audit


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The processes of selecting items from production lotto evaluate in product audit is referred to assampling or Taking a sample.

A sample is a subset of a production lot. It includes afew items removed from a production or shipping lotthat are assumed to represent the overall range ofquality.

Selecting a sample is a critical process in developinga reasonably confident picture of the quality andconsistency of the entire lot.


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The sample depends on the size of the lot, requiredacceptable level of quality, the buyers confidence inthe supplier or vendor and the type of defects that

may occur. Two out come:

Result

Acceptable Rejected


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Selection of sample

If the companys inspection plan includes in-processinspection during production and 100% materialsinspection, then a final in-depth inspection of everyitem from production is not necessary. A sample ofthe lot described as a statistical or random sampling

will help the company verify that quality is or is notacceptable.


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Selection of sample

If the sample is drawn from the lot so that each itemhas an equal chance of being selected, then anyproblems, errors, or flaws will more than likely bepresent in the sample. Thus the sample represent thelot and an evaluation of the sample will provideessentially the same type of information as a fullinspection, with a minimal investment of time and

labor.


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Selection of Sample

Incase a sample is a selected set of products thatrepresent every style, color, and size in theproduction lot based on its distribution. Thus thesample should reflect the numerical distribution ofthe lot.

Samples should be free of bias.


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Types of Samples

Random Sample: samples that are free of bias. Eachproduct in a lot has an equal chance of being selectedfor inspection regardless of its sequence ofproduction, color, size, style, location in boxes, anyother factor of production, packaging orconvenience.

Randomly select a set of numbers and pull the

corresponding products for assessing productquality.


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Types of Samples

Representative Sample: Includes all styles, colors,sizes and other planned variations in the product.For apparel representative lots are usually selected,

but they are not automatically random unless eachitem in the lot had an equal chance of being selected.

Products for a random or representative sampleshould be selected so that they are not all from the

same box, location in a stack or box, produced on thesame machine, or represent the same size or samecolor.


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Types of Samples

Convenience sample: means that the sample item areselected because they were easier to select comparedto other possible samples.

Convenience sample should be avoided wheneverpossible because they are not random and are notrepresentative of entire lot.


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Types of Samples

Stratified sample: the lot is stratified in to layers.Each layer is subdivided into cubes. If a cube isidentified to be included in the sample, then everyitem within the cube is pulled for the sample.

Stratified samples are used when a large, supposedlyhomogenous lot is sampled because it facilitates theprocess of pulling or taking the sample.


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Types of Samples

Constant percentage sample: the same percentage isused regardless of lot size to determine the numberof units to be sampled. Ex: 1% from the totalproduction

This type of plan does not offer adequate protectionfor small lots and offers too much protection forlarge lots.

Statistically determined sampling plans are not

dependent on the size of the lot. These plans aremore efficient and less expensive to operate thanconstant percentage sampling plan.


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Types of Samples

Systematic sample: selects units from equallyoccurring locations or at equal intervals of time.

It works well with continuously operationg

production lines where same product is produced forweeks or months at a time.


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Sampling plan

A sampling plan describes how to select a reasonable numberof products to represent the production unit or lot based oncolor, size, style and other dimensions. Good sampling plansare critical to the process of acceptance sampling.

Acceptance sampling is the inspection and evaluation ofsample products selected from production lots for identifiedquality characteristics after the product has been produced.

Many apparel industries use a document developed by thedepartment of defense. Military standard 105E or MIL STD

105E, was used as the basis for sampling and for settingacceptable limits. However, since that standard was canceled in1995, many companies use the commercial equivalent

ANSI/ASQZ1.4-2003, or ISO 2859- (1999)


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Why?

If sample consists of too few items the sample is notrepresentative costs for inspecting the same may below and result may be invalid.

If the sample consists of too many items the cost forinspecting the sample increases drastically without acorresponding increase in confidence in the resultsof the audit.


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Sampling plans assume that the product represents a lotproduced from the same materials, using the sameassembly processes, based on the same specifications andreceiving the same processing. In this case product could

refer to materials, components or end products. Themajor assumption of sampling plan is the products arehomogeneous or essentially alike throughout the lot.

Variations in materials, color or styles that are includedas a part of product specifications and standards are

allowed and are considered part of the productdescription. The audit is designed to determine thedegree to which accidental variation within or betweenproducts exists.


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An operating characteristic curve

Is a plot of the probabilities of accepting a lot giventhe largest number of non conformances allowed in asample size n. standard tables are available toidentify the number of units to pull for a selectedsample plan. These tables make it easier todetermine samples sizes than calculating thenumbers using statistical equations.


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Types of Sampling Plan

Several types of sampling plans are available. Factors for the selection isbased on Record keeping documents - a performance and delivery history of

suppliers. (Deciding on the past performance History) Lot by lot basis:- samples are pulled from each production lot. Plans

differ for each lot if combinations between lots differ. It is used for new

company where no established history is available. Used for fashion goodsbecause materials, styling and assembly change frequently. Lot-by-Lotacceptance sampling by attribute in which sample from each lot isinspected according to attributes. (minor differences)

Attributes are specific criteria such as size, appearance, function of closures,color matching and seam appearance. Each products adherence to standardand specifications is assessed.

Eg: two shirt production lots identical except for the pattern of the printwould undergo lot-by-lot acceptance sampling by attribute. (fabric, color,etc)


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Types of Sampling Plan

skip lot basis, some production lots are not sampled. It is used todecrease sampling. This is common with producers of consistentlyhigh-quality products, when production history has beenestablished at high levels or when materials, styling and assemblychange infrequently, as with many basic goods.

Ex: basic bath linens, some undergarments, and basic T-shirts would

be candidates for a skip lot basis sampling plan. Continuous production sampling is used when products or

processes are consistent for long periods of time. In continuousproduction, the assembly line may not stop for weeks or months at atime. The sample is inspected to verify that product quality has notchanged and that products continue to meet standards and

specificationsEx: in textile and apparel industry is that of basic nylon pantyhose.Samples are pulled from the line on a random basis to check forproduct consistency and to verify that product quality does not vary.


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In an ideal sampling plan, the samples represent fullyand accurately the quality of the lot. The audit wouldresult in the rejection of all lots worse than the standardand acceptance of all lots equal to or better than the

standard.A standard product or standard is one that meets allspecifications and company or product requirements.

How ever there is a possibility exists that acceptable lotswill be rejected (suppliers risk or alpha) and inferior lotswill be accepted(consumer risk or beta). Supplier risk isknown as Type 1 error and Consumers risk is known asType 2 error.


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Single sampling plan is the total number ofsamples products inspected and the total size of thesample are equal. Only sample is pulled forinspection. Acceptance or rejection of the productionlot is based on adherence to standards.

Acceptance means that the lot meets or exceedsstandards and specifications and the buyer accepts the

lot.Rejection means that the lot did not meet standardsand specifications and that the buyer rejects the lot.


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When Double sampling plan is used, it means that aproblem was detected with the first sample. The number ofsample production to be inspected increased. The totalnumber of sample products evaluated is related to the degreeto which the original sample did not meet the standards. In

other words an additional sample is taken and evaluated.Acceptance or rejection is based on the cumulative results ofboth samples.

Multiple sample plans may use as many as seven samplesets before a final decision regarding the disposition of theproduction lot is reached. Multiple sample plans are not

common with textile products. These plans (double andmultiple) means that more items will be inspected. It does notmean that the inspectors look at each item more closely orapply more stringent standards and specifications.


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Advantages and Disadvantages of Sampling

Working with a sample from a lot is moreeconomical than 100% inspection.


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sampling lot in final audit

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