RADIOLIGAND ASSAY

In radioimmunoassay and immunoradiometric assay, potency estimation involves the relation between counts of radioactivity and dose. Estimation of all the parameters under the supposition (supported by empirical evidence) is discussed; the variance of a count is proportional to UJ, where U is the mean count at a dose and J is a parameter that almost certainly lies between 1.0 and 2.0. Estimation is very robust, both in respect of the value taken for J and over alternative forms of least squares and maximum liklihood procedures. Special attention is given to whether the assay uses one or more doses of each test preparation, the former having important limitations but permitting some simplification of formulae. Requirements for a comprehensive computer program, suitable for routine use by assayists lacking statistical expertise and designed to produce potency estimates for a series of test preparations in one assay, are described. Data from an estradiol assay are used to illustrate various points.