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Term  Definition  Source of Definition 
Acceptance sampling  Sampling inspection in which decisions are made to accept or reject product.; also the science that deals with procedures by which decisions decisions to accept or reject are based on the results of the inspection of samples.  Glossary and Tables for Statistical Quality Control  ASQC 
Comment: Typical uses of acceptance sampling
in manufacturing include making acceptance decisions about incoming raw materials lots,
inprocess sublots, and finished product lots. Acceptance sampling software


Acceptance sampling plan  A specific plan that states the sample size or sizes to be used and the associated acceptance and rejection criteria.  Glossary and Tables for Statistical Quality Control  ASQC 
Comment: Most acceptance sampling plans in
use are either attributes plans and variables plans. Acceptance sampling software


AOQ curve  Acronym for Average Outgoing Quality. Useful to evaluate
sampling plan applications where rejected lots are rectified by replacing or reworking
defective items. The AOQ curve is the average quality of outgoing product as a function of
the incoming quality. Examples: AOQ curve for defectives AOQ curve for defect counts AOQ curve for variables fraction nonconforming 

Comment: AOQ is the quality of an average
outgoing lot. Therefore, you should expect half of the lots to be worse than AOQ. The AOQ
calculation does not consider that the incoming quality usually varies.


AOQL  Acronym for Average Outgoing Quality Limit. The maximum AOQ over all possible values of incoming product quality, for a given acceptance sampling plan.  Glossary and Tables for Statistical Quality Control  ASQC 
Comment: Maximum of the AOQ curve. See AOQ.


AQL  Acronym for Acceptable Quality Level. As used in the
development of twopoint acceptance sampling plans, the values of AQL and alpha jointly
define the producers point of the operating characteristic curve. Graph showing the producers point. If the value of a quality characteristic of a particular lot is exactly equal to the AQL of it's acceptance sampling plan, the probability that the plan will accept the lot is (Pa=1alpha). Example of specifying AQL For a discussion of common confusions about AQL, see AQL Primer. 
"Glossary and Tables for Statistical Quality Control"  ASQC. 
Comment: This definition of AQL is
statistically exact and appropriate for use with twopoint sampling plans, as supported by
the software of H & H Servicco Corp. On the other hand, a more vague definition of AQL is typically used by documents that support onepoint sampling plans. The most common of such documents are: MilStd105, MilStd414, ANSI/ASQC Z1.4, ANSI/ASQC Z1.9 These onepoint sampling plans do not make use of the consumer's point  they do not address the issue of accepting lowquality lots. They are particularly vulnerable to this for small sample sizes. 

ARL curve  Acronym for Average Run Length. ARL is the average number of
accepted lots between rejections. The ARL curve is a plot of ARL as a function of lot
quality level. Examples: ARL curve for defectives ARL curve for defect counts ARL curve for variables fraction nonconforming 

Comment: Use the ARL curve to assess the impact of an
acceptance sampling plan on smoothness operations.


ASN curve  Acronym for Average Sample Number. ASN is the average number
of sample units inspected per lot in reaching decisions to accept or reject. The ASN curve
is a plot of ASN versus lot quality. Examples: ASN curve for defectives ASN curve for defect counts ASN curve for variables fraction nonconforming 
Glossary and Tables for Statistical Quality Control  ASQC 
Comment: Use ASN curves to evaluate
sequential sampling plans to anticipate the amount of inspection that each plan will
require.


Audit sampling  Sampling in which the goal is to estimate the value a quality characteristic but not provide a firm decision rule. The sample size n is chosen to provide a desired margin of error of the estimate.  
Comment: Many audit sampling situations
involve more than one category, each having a different sample size. The categories
having the smaller sample sizes will have estimates with larger margins of error.
Conversely, the categories having the larger sample sizes will have estimates with smaller
margins of error. Audit sampling software


Margin of Error  The sampling error of the estimated statistic. The margin of
error is usually expressed as half the the width of a confidence interval. Examples: p' plus or minus ME Xbar plus or minus ME where ME=Margin of Error Audit Sample Planner develops sampling plans based on the margin of error. 

OC curve  Acronym for Operating Characteristic Curve. A curve showing,
for a given sampling plan, the probability of accepting a lot, as a function of the lot
quality level. It is knowledge (by the person who designs or selects the plan) of the oc
curve that makes an acceptance sampling plan statistically
valid. Examples: OC curve for defectives OC curve for defect counts OC curve for variables fraction nonconforming OC curve for MTBF OC curve for reliability 
Glossary and Tables for Statistical Quality Control  ASQC 
Comment: The OC curve is fundamental to the
twopoint method of developing acceptance sampling plans. Twopoint method


RQL  Acronym for Rejectable Quality Level. As used in the
development of twopoint acceptance sampling plans, the values of RQL and beta jointly
define the consumers point of the operating characteristic curve. Graph showing the consumers point. If the value of a quality characteristic of a particular lot is exactly equal to the RQL of it's acceptance sampling plan, the probability that the plan will accept the lot is (Pa=beta). Example of specifying RQL The literature contains other terms having the same meaning as RQL. These are LQ (limiting quality) and LTPD (lot tolerance percent defective). 
Glossary and Tables for Statistical Quality Control  ASQC. See LTPD. 
Sequential Analysis, Sequential Sampling 
The technique by which we build up our sample one item at a
time, and after inspecting each item, ask ourselves: "Can we be sure enough to accept
or reject this batch on the information so far collected?" Its value is in enabling reliable conclusions to be wrung from a minimum of data. This was deemed sufficient to require that it be classified "Restricted " within the meaning of the Espionage Act during the war of 193945. 
Facts from Figures  M. J. Morony 
Comment: Used for lotbylot
acceptance plans for applications needing the minimum possible average sample numbers.


Statistically Valid  An acceptance sampling plan is statistically valid when the person who designs or selects it knows the probabilities that the plan will accept lots that were manufactured to various quality levels. These probabilities are shown by the operating charactistic curve (oc curve) 