Z94.16 - Quality Assurance & Reliability
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PARAMETER. A quantity used in describing the probability distribution of a random variable. [1: 1.12]
PERCENT CHART. A control chart for evaluating the process in terms of the percent of the total number of units (areas of opportunity) in a sample in which a nonconformity of a given classification occurs. [2: 3.3.8].
POWER OF A TEST. The probability of not committing an error of the second kind. Note: Thus, it is the probability, usually designated (1-ß), of rejecting the null hypothesis when this hypothesis is false. [1: 2.79].
PRECISION. The closeness of agreement between independent test results obtained under stipulated conditions. Notes: (1) Precision depends only on the distribution of random errors and does not relate to the true value or the specified value. (2) The measure of precision usually is expressed in terms of imprecision and computer as a standard deviation of the test results. Less precision is reflected by a larger standard deviation. (3) "Independent test results" means results obtained in a manner not influenced by any previous result on the same or similar test object. Quantitative measures of precision depend critically on the stipulated conditions. Repeatability and reproducibility conditions are particular sets of extreme stipulated conditions. [1: 3.14]
PREVENTIVE ACTION. Action taken to eliminate the causes of a potential nonconformity defect or other undesirable situation in order to prevent occurrence. [3: 4.13]
PROBABILITY. A basic concept which may be taken either as expressing in some way a "degree of belief", or as the limiting frequency in an infinite random series. Both approaches lead to much the same calculus of probabilities. [1: 1.1].
PROBABILITY DISTRIBUTION (OF A RANDOM VARIABLE). A function giving the probability that a random variable takes any given value or belongs to a given set of values. Note: The probability on the whole set of values of the random variable equals 1.[ 1: 1.3]
PROCEDURE. Specified way to perform an activity. Notes: (1) In many cases, procedures are documented. (2) When a procedure is documented, the term "written procedure" or "documented procedure" is frequently used. [3: 1.3]
PROCESS. Method of operation in any particular stage of any element, group of elements, or total aspect of production or service. Note: It is necessary to distinguish between an individual and an overall process. [2: 1.1.1]
PROCESS CAPABILITY. A statistical measure of inherent process variability for a given characteristic. Notes: (1)Standard measures of process capability have not achieved consensus at the present time. some examples are: (a)the standard deviation (s) or the range, or a multiple thereof based upon the inherent variability; (b)a composite value of the component due to inherent variability and a component due to small assignable causes; (c)a composite value of a multiple of the standard deviation of inherent variability based upon an individual process (which can be denoted by ?), plus an acceptable small range allowed for shifts due to assignable causes. (2) When using the term 'process capability,' it is essential to state which measure is being used (in appropriate cases si, or st may be specified). [2: 3.2.3]
PROCESS IN CONTROL; STABLE PROCESS. A process in which each of the quality measures (e.g. the average and variability or fraction nonconforming or average number of nonconformities of the product or service) is in a state of statistical control. Note: Statistical control is usually assessed by using control charts. [2: 3.1.6]
PROCESS INSPECTION. Inspection of a process by examination of the process itself or of the product characteristics at the appropriate stage(s) of the process. [ 1: 1.2.2]
PROCESS QUALITY CONTROL; PROCESS CONTROL. That part of quality control that is concerned with maintaining the product, process or service characteristics, within specified limits. [2: 1.1.6]
PRODUCER'S RISK (PR). For a given sampling plan, the probability of non-acceptance of a lot when the lot or process quality level (e.g. the fraction nonconforming) has a value stated by the plan as acceptable [e.g. acceptable quality level (AQL)].[ 2: 2.6.7]
PRODUCER'S RISK QUALITY (PRQ). A lot or process quality level which in the sampling plan corresponds to a specified producer's risk. Notes: (1) The type of operating characteristic curve should be specified. (2) A special case of this is 'acceptable quality level' when the operating characteristic curve is type B.[2: 2.6.9]
PRODUCER'S RISK POINT (PRP). A point on the operating characteristic curve corresponding to the producer's risk. Note: The type of operating characteristic curve should be specified. [2: 2.6.8]
(PRODUCTION) BATCH. A definite quantity of some commodity or service produced at one time under conditions that are presumed uniform. Note: The circumstances under which the conditions can be presumed uniform cannot be generally stated; for example, a change in the material or tool used or an interruption in the manufacturing process can give rise to different conditions. [2: 1.3.4]
PROPORTION CHART; FRACTION CHART. A control chart for evaluating the process in terms of the proportion (or fraction) of the total number of units (areas of opportunity) in a sample in which a nonconformity of a given classification occurs. [2: 3.3.7]
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