Z94.16 - Quality Assurance & Reliability
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SAMPLING. The process of drawing or constituting a sample. [2: 2.1.2]
SAMPLING ERROR. That part of the estimation error which is due to the fact that only a sample of size less than the population size is observed. [1: 2.53]
SAMPLING FRAME. A list, compiled for sampling purposes, which designates the items of a population to be considered in a study. [1: 2.4]
SAMPLING INSPECTION. The inspection of products or services using samples (as distinct from 100% inspection).[2: 2.2.1]
SAMPLING INTERVAL. In periodic systematic sampling, an interval at the end of which a sample is taken. [2: 2.1.8]
SAMPLING PLAN. A specific plan which states the sample size(s) to be used and the associated criteria for accepting the lot. Notes: (1) A criterion is, for example, that the number of nonconforming items is less than or equal to the acceptance number. (2) The sampling plan does not contain the rules on how to take the sample. [2: 2.3.3]
SAMPLING PROCEDURE. Operational requirements and/or instructions relating to the use of a particular sampling plan; i.e. the planned method of selection, withdrawal and preparation of sample(s) from a lot to yield knowledge of the characteristic(s) of the lot. [2: 2.3.2]
SAMPLING SCHEME. A combination of sampling plans with rules for changing from one plan to another. Note: Some schemes have switching rules for automatic change to tightened inspection plans or reduced inspection plans or change to 100% inspection. [2: 2.3.4]
SAMPLING SYSTEM. A collection of sampling schemes, each with its own rules for changing plans, together with criteria by which appropriate schemes may be chosen. [2: 2.3.5]
SAMPLING UNIT. (1)One of the individual items into which a population is divided. (2) A quantity of product, material or service forming a cohesive entity and taken from one place at one time to form part of a sample. Notes: (1) A sampling unit may contain more than one item to be tested, e.g., a packet of cigarettes, but one test result or observation will be obtained from it. (2) The unit of a product may be a single item, a pair or a set of items, or it may be a specified quantity of material, such as a length of round brass rod, a volume of paint, or a weight of coal. It need not be the same as the unit of purchase, supply, production, or shipment. [2: 1.3.3].
SAMPLING WITH REPLACEMENT. Sampling in which each sampling unit taken and observed is returned to the population before the next sampling unit is taken. Note: In this case the same sampling unit may appear several times in the sample. [1: 4.6]
SAMPLING WITHOUT REPLACEMENT. Sampling in which sampling units are taken from the population once only or successively without being returned to the population.[1: 4.7]
SAMPLE. One or more sampling units taken from a population and intended to provide information on the population. [2: 2.1.1]
SAMPLE SIZE. Number of sampling units in a sample. [ 2: 2.1.3]
SAMPLE STANDARD DEVIATION CHART; S CHART. A control chart for evaluating the variability within a process in terms of the sample standard deviation, s, of the sub-group. [2: 3.3.14]
SCREENING INSPECTION. 100% inspection of material or items of a product, with rejection of all items or portions found nonconforming. Notes: (1) Screening inspection might only be concerned with one particular kind of nonconformity. (2) Screening may be carried out for the purpose of removing nonconforming items from a lot or batch which was not accepted. [2: 1.2.6]
SEQUENTIAL SAMPLING INSPECTION. Sampling inspection in which, after each item has been inspected, the decision is made according to a defined rule based on the cumulative evidence of all the items from that lot inspected so far: to accept the lot, not to accept it, or to inspect another item. Note: The total number of items to be inspected is not fixed in advance but a maximum number is often agreed upon. [2: 2.4.4]
SERVICING. The replenishment of consumables needed to keep an item in operating condition, but not including any other preventive maintenance or any corrective maintenance. [7]
SEVERITY OF SAMPLING. The degree of discrimination within a sampling scheme for changing from a normal to a reduced (tightened) sampling plan if the quality of the submitted product or service improves (deteriorates). Note: This term should not be confused with inspection level, which is independent of switching rules. [2: 2.5.2]
SHEWHART CONTROL CHART. A control chart to show if a process is in statistical control. Note: It may be a chart using attributes (e.g. proportion nonconforming) for evaluating a process, or it may be a chart using variables (e.g. average and range) for evaluating a process. [2: 3.3.3]
SIGNIFICANCE LEVEL (OF A TEST) The given value which is the upper limit of th etype 1 error probability. Note: The significance level is usually designated as a. (1: 2.70)
SIGNIFICANT RESULT (AT THE CHOSEN SIGNIFICANCE LEVEL a). The result of a statistical test which leads to the rejection of the null hypothesis. If the hypothesis is not rejected, the result is not significant. Note: When the test result is called statistically significant, this means that the result is out of the range of values that are likely from random effects if the null hypothesis is true. It does not necessarily mean that this has physical or economic importance.(1: 2.84)
SIGNIFICANCE TESTING. Statistical appraisal of the outcomes of sampling to note whether or not, at a certain level of risk, the results represent real effects or chance fluctuations of sampling and measurement.
SIMPLE RANDOM SAMPLE. A sample of n items taken from a population of N items in such a way that all possible combinations of n items have the same probability of being taken. [2: 2.1.4]
SINGLE SAMPLING INSPECTION. Sampling inspection in which the decision, according to a defined rule, to accept or not to accept a lot is based on the inspection results obtained from a single sample of predetermined size n. [2: 2.4.1]
SKIP-LOT SAMPLING INSPECTION. Sampling inspection in which some lots in a series are accepted without inspection, when the sampling results for a stated number of immediately preceding lots meet stated criteria. [2: 2.4.9]
SPECIFICATION. Document stating requirements. Notes: (1) A qualifier should be used to indicate the type of specification, such as product specification, test specification. (2) A specification should refer to, or include, drawings, patterns or other relevant documents and indicate the means and the criteria whereby conformity can be stating. [3: 3.14]
STANDARD DEVIATION (OF A RANDOM VARIABLE, OR OF A PROBABILITY DISTRIBUTION). The positive square root of the variance of the random variable. [1: 1.23]
STANDARD DEVIATION (OF A SAMPLE). The positive square root of the variance of the sample. Note: The sample standard deviation is a biased estimator of the population standard deviation. [1: 2.34]
STANDARD ERROR. The standard deviation of an estimator. [1: 2. 56]
STATE OF STATISTICAL CONTROL. A state in which the variations among the observed sampling results can be attributed to a system of chance causes that does not appear to change with time. Note: Such a system of chance causes will generally behave as though the results are simple random samples from the same population. [2: 3.1.5]
STATISTIC. A function of the sample random variables. Note: A statistic, as a function of random variables, is also a random variable and as such it assumes different values from sample to sample. The value of the statistic obtained by using the observed values in this function may be used in a statistical test or as an estimate of a population parameter such as a mean or a standard deviation. [1: 2.45]
STATISTICAL QUALITY CONTROL. That part of quality control in which statistical techniques are used. Notes: (1) These techniques include the use of frequency distributions, measures of central tendency and dispersion, control charts, acceptance sampling, regression analysis, tests of significance, etc. (2) When statistical quality control is used to control the operation of a process rather than to control the quality of materials supplied, the term 'statistical process control' is often used. [2: 1.1.7]
STATISTICAL TEST. A statistical procedure to decide whether a null hypothesis should be rejected in favour of the alternative hypothesis or not rejected. Notes: (1) The decision on the null hypothesis is taken based on the value(s) of an appropriate test statistic or statistics. Since the test statistic is a random variable, there is some risk of error when the decision is taken. (2) Generally, a test assumes a priori that certain assumptions are fulfilled (for example, assumption of independence of the observations, assumption of normality, etc). [1: 2.65]
STEP STRESS TEST. A test consisting of several increasing stress levels applied sequentially for periods of equal time duration to an item. During each period a state stress level is applied and the stress level is increased from one step to the next. [4: 191-14-08]
STRATIFICATION. The division of a population into mutually exclusive and exhaustive subpopulations (called strata), which are thought to be more homegeneous with respect to the characteristics investigated than the total population.[1: 4.13]
STRATIFIED RANDOM SAMPLING. The process of selecting a simple random sample from each of the population strata. [1: 4.14]
STRATUM. A group of units from a population, sub-population, usually defined by relevant population characteristics. [1: 4.13]
SUB-GROUP (MEASUREMENT SENSE). One of the sets of groups of observations obtained bysubdividing a larger group of observations. [2: 1.3.10]
SUB-GROUP (OBJECT SENSE). One ofthe sets of items or quantities of material obtained by subdividing a larger group of items or quantities of material.[ 2: 1.3.9]
SURVEILLANCE. Continual monitoring and verification of the status of an entity and analysis of records to ensure that specified requirements are being fulfilled. [3: 4.7]
SURVIVABILITY. The measure of the degree to which an item will withstand hostile man-made environment and not suffer abortive impairment of its ability to accomplish its designated mission. [7]
SWITCHING RULES. Instructions within a sampling scheme for changing from one sampling plan to another of greater or less severity (e.g. normal, reduced, or tightened inspection or discontinuance of acceptance), based on demonstrated quality level history. [2: 2.5.3].
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