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Parallel-Line Assay

  1. Carol K. Redmond

Published Online: 15 JUL 2005

DOI: 10.1002/0470011815.b2a06020

Encyclopedia of Biostatistics

Encyclopedia of Biostatistics

How to Cite

Redmond, C. K. 2005. Parallel-Line Assay. Encyclopedia of Biostatistics. 6.

Author Information

  1. University of Pittsburgh, Pittsburgh, PA, USA

Publication History

  1. Published Online: 15 JUL 2005


Parallel-line assays are the most common form of indirect analytical assays. The aim is to estimate the potency of substance under test relative to the potency of a standard. The test and standard preparations are administered at several dose levels. The key assumption is that the expected response for a given dose of the test preparation is the same as that which would be obtained from the standard preparation administered at a dose that is ρ times the given dose: ρ is known as the relative potency. It is further assumed that the expected response is linearly related to the logarithm of the dose. If this obtains, the graphs of expected response against log dose for the test and standard preparations will give parallel lines. The response can be continuous, in which case estimation is through a linear model, or quantal, in which case analysis usually assumes a logistic model. The estimator of ρ is defined in terms of ratios of regression coefficients and interval estimates are often obtained by use of Fieller's theorem.


  • dose metameter;
  • Fieller's theorem;
  • linear model;
  • logistic model;
  • quantal response;
  • relative potency;
  • slope-ratio assay