Qualitative (Attribute) & Quantitative (Variable) Testing

Qualitative analysis 

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Measurement uncertainty:

e.g. uncertainty about the identity of:

  • barcode
  • molecule (e.g. Salicylamide instead of Aspirin)
  • information on a screen

due for instance to poor visibility.

Qualitative measurement results are often quoted on scales – such as the ordinal – which cannot be analysed in terms of differences and standard deviations [Svensson 2001, Bashkansky and Gadrich 2010] familiar with quantitative measurement uncertainty estimates by variable.

Uncertainty estimates in qualitative measurements rather attempt to express the fuzziness or lack of clarity in patterns and shapes, as can be expressed in basic measures of information content.

Qualitative measurement uncertainties do reveal themselves, however – as clearly as their more quantitative counterparts – in risks of incorrect decisions of compliance when a quality characteristic of an entity is compared with a specification limit.

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Relation between Attribute and Variable Testing

Testing by variable can be seen as a subset of the more general testing by attribute: i.e., where the (quality) characteristic of the entity under test is an attribute which can be a variable.

The more general attribute testing includes not only ‘quantitative’, by variable, but also ‘qualitative’ measurements of product characteristics, as perceived for example with the human senses.

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References

Bashkansky E and Gadrich T 2010 ”Some metrological aspects of ordinal measurements”,  Accred Qual Assur 15, pp. 331 – 6 doi: 10.1007/s00769-009-0620-x

ISO 2859-1:1999 “Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection”

ISO 3951-1:2005 “Sampling procedures for inspection by variables — Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a single quality characteristic and a single AQL”

Klir G J and Folger T A 1988 “Fuzzy sets, uncertainty and information”, Prentice Hall, New Jersey ISBN 0-13-345984-5

L R Pendrill, B Berglund et al. 2010 “Measurement with Persons: A European Network“, NCSLi Measure, Vol. 5 No. 2 • June 2010, pp. 42 – 54

E Svensson 2001, “Guidelines to statistical evaluation of data from rating scales and questionnaires”, J Rehab Med; 33: 47–48

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