Average outgoing quality (AOQ): The expected average quality
level of outgoing product for a given value of incoming product
quality.
Average outgoing quality limit (AOQL): The maximum average
outgoing quality over all possible levels of incoming quality for a given
acceptance sampling plan and disposal specification.
Acceptable quality level (AQL): In a continuing series of lots, a
quality level that, for the purpose of sampling inspection, is the limit of
satisfactory process average.
Acceptance number: The maximum number of defects or defectives
allowable in a sampling lot for the lot to be acceptable.
Acceptance sampling: Inspection of a sample from a lot to decide
whether to accept that lot. There are two types: attributes sampling
and variables sampling. In attributes sampling, the presence or
absence of a characteristic is noted in each of the units inspected. In
variables sampling, the numerical magnitude of a characteristic is
measured and recorded for each inspected unit; this involves
reference to a continuous scale of some kind.
Acceptance sampling plan: A specific plan that indicates the
sampling sizes and associated acceptance or nonacceptance criteria
to be used. In attributes sampling, for example, there are single,
double, multiple, sequential, chain and skip-lot sampling plans. In
variables sampling, there are single, double and sequential sampling
plans. (For detailed descriptions of these plans, see the standard
ANSI/ISO/ASQ A3534-2, Statistics--Vocabulary and
Symbols--Statistical Quality Control.)
Binomial distribution: A discrete distribution characterized by
having an infinite sample size or a steady stream of production, and
have outcomes equal to success or failure.
Probability of exactly an event is equal to:
P(x) =(n!/x!(n-x)!) px (1-p)n-x
x = number of defects
n = sample size
p = probability of unit being defective
Combination: The number of distinct combinations of n distinct
objects taken r at a time is denoted by the symbol Cnr.
Cnr = n!/ r!(n-r)!
Defect: A product's or service's nonfulfillment of an intended
requirement or reasonable expectation for use, including safety
considerations. There are four classes of defects: class 1, very
serious, leads directly to severe injury or catastrophic economic loss;
class 2, serious, leads directly to significant injury or significant
economic loss; class 3, major, is related to major problems with
respect to intended normal or reasonably foreseeable use; and class
4, minor, is related to minor problems with respect to intended normal
or reasonably foreseeable use (see also "blemish," "imperfection"
and "nonconformity
Defect – critical: leads directly to severe injury or catastrophic
economic loss; leads directly to significant injury or significant
economic loss; class
Defect – major: related to major problems with
respect to intended normal or reasonably foreseeable use
Defect – minor: is related to minor problems with respect to intended
normal or reasonably foreseeable use (see also "blemish,"
"imperfection" and "nonconformity
Defective: A defective unit; a unit of product that contains one or
more defects with respect to the quality characteristic(s) under
consideration.
Factorial: Number multiplied by all numbers contained in the
sequence. For example 3! = 3 * 2* 1 = 6.
0! = 1
Fraction defective: For a sample, the fraction defective is the
number defective (np) divided by the sample size (n).
Inspection: Measuring, examining, testing and gauging one or more
characteristics of a product or service and comparing the results with
specified requirements to determine whether conformity is achieved
for each characteristic.
Nonconformance: A unit containing a non-conformity.
Nonconformity: The non-fulfillment of a specified requirement (see
also "blemish," "defect" and "imperfection").
Number defective: In a sample it is the number of units not
conforming to the specification. For a distribution, it is the sample
size times the fraction non-conforming.
Operating characteristic curve (OC curve): A graph to determine
the probability of accepting lots as a function of the lots' or
processes' quality level when using various sampling plans. There
are three types: type A curves, which give the probability of
acceptance for an individual lot coming from finite production (will not
continue in the future); type B curves, which give the probability of
acceptance for lots coming from a continuous process; and type C
curves, which (for a continuous sampling plan) give the long run
percentage of product accepted during the sampling phase.
P chart: See "percent chart."
p-value: the probability of obtaining a value of the test statistic as
extreme as, or more extreme than, the actual value obtained when
the null hypothesis is true.
The smallest level of significance, alhpa, at which the null hypothesis
may be rejected using the obtained value of the test statistic.
Percent chart: A control chart for evaluating the stability of a
process in terms of the percentage of the total number of units in a
sample in which an event of a given classification occurs. The
percent chart is also referred to as a proportion chart.
Percent defective: 100 * fraction defective.
Permutation: An ordered arrangement of n distinct objects. The
number of ways an ordering of n objects taken r at a time is
designated by the symbol Pnr.
Pnr = n!/(n-r)!
Poission distribution: A discrete distribution obtained by counting
the nonconformities in physical unit or units of a given size;
sometimes called the region of operation.
Probability of x outcomes:
P(x) = (npx e-np)/x!
e is the mathematical value 2.71828 etc
n is the size of the region of operation
p is the probability of single occurrence
x is the number occurrences of interest
Probability of acceptance: The probability that a lot will be
accepted.
Probability of rejection: The probability that a lot will be rejected.
Process capability of a discrete distribution: A statistical measure
of the inherent process variability for a given characteristic. The most
widely accepted value for process capability for discrete distributions
is the mean value.
Random sampling: A commonly used sampling technique in which
sample units are selected so that all combinations of n units under
consideration have an equal chance of being selected as the sample.
Rectification: The process of exchanging all defective units in a lot
with conforming units. The result of this process is to provide a lot
which achieves AOQL.
RQL – Reject Quality Level : On an operating characteristic curve it
locates the unsatisfactory quality level. Usually at Pa = .1.