Lot quality assurance sampling

Lot quality assurance sampling (LQAS) is a random sampling methodology, originally developed in the 1920s ^[1] as a method of quality control in industrial production. Compared to similar sampling techniques like stratified and cluster sampling, LQAS provides less information but often requires substantially smaller sample sizes.

Summary

LQAS, sometimes called "acceptance sampling",^[2] involves taking a small random sample from each set of items in the population, and testing each sampled item to determine whether it meets a predetermined standard of quality. LQAS is functionally identical to stratified sampling (where each lot is a single stratum), but requires smaller samples because it does not attempt to construct a precise estimate of population parameters. Instead, after sampling, a researcher using LQAS performs a hypothesis test to determine whether the number of elements of interest in each lot (e.g. defective units in manufacturing, or persons with a particular medical condition in epidemiology) is likely to be greater than a predetermined threshold.

Use

LQAS was originally designed for use in manufacturing, where it provided a way to perform statistically valid quality-assurance testing at minimum cost. In the context of modern research, LQAS has become an accepted sampling method in the fields of public health and international development. For example, in 1996 the World Health Organization issued a document^[3] describing LQAS, and recommended it for use in surveys to determine the number of children immunized against disease.

Notes

1. Dodge, H.F., & Romig, H.G. (1929). "A method of sampling inspection." Bell System Technical Journal 8: 613–31.
2. Lemeshow, S. & Taber, S. (1991). Lot quality assurance sampling: single- and double-sampling plans". World Health Statistics Quarterly, 44(3), 115-32. PMID 1949879.
3. Robertson, S. (1996). Monitoring immunization services using the Lot Quality Technique. World Health Organization: Geneva.

References

• Alberti, K.P., Guthmann, J.P., Fermon, F., Nargaye, K.D., & Grais, R.F. (2008). "Use of Lot Quality Assurance Sampling (LQAS) to estimate vaccination coverage helps guide future vaccination efforts". Transactions of the Royal Society of Tropical Medicine and Hygiene., 102(3), 251-4.

• Biedron, C.; Pagano, M.; Hedt, B. L.; Kilian, A.; Ratcliffe, A.; Mabunda, S.; Valadez, J. J. (2010). "An assessment of Lot Quality Assurance Sampling to evaluate malaria outcome indicators: Extending malaria indicator surveys". International Journal of Epidemiology 39 (1): 72–79. doi:10.1093/ije/dyp363. PMC 2912491. PMID 20139435.