Testing for a treatment effect in the presence of nonresponders.
Good (1979, Biometrics 35, 483-489) introduced a new randomization test for the two-sample problem where a proportion 1 - p of the treatment group does not respond to the treatment, and suggested that the Wilcoxon test is not effective for this situation. We show to the contrary that the Wilcoxon test is quite useful when p greater than or equal to .6 and point out an error in his definition of a one-tailed randomization test.
Detection of a treatment effect when not all experimental subjects will respond to treatment.
Non-responders attenuate average response an inflate sample variance, reducing the power of standard parametric tests. A new Fisher's type randomization test, which has no parametric analogue, is recommended when not all subjects may be capable of responding to treatment. The new test was evaluated by Monte Carlo means and applied to drug abuse data and to virus titre data. In most trial applications the new test proved to be more sensitive to treatment effects than Student's t.
Effects of altered porphyrin synthesis on brain neurochemistry.
Lead is one of several environmentally significant substances which alter porphyrin synthesis in several organs. Biochemically, the consequences of both acute and chronic lead exposure, at relatively low dose, are increases in tissue and plasma levels of the porphyrin precursor aminolevulinic acid (ALA) and inhibition of the enzyme ALA dehydrase. These effects are considered for their possible role in the neurotoxicity associated with lead exposure. The effects of lead, on porphyrin metabolism and on neurochemistry and behavior, are compared to those associated with exposure to the "suicide" inhibitor of ALA dehydrase, succinylacetone. Similarities in both porphyrinopathy and in associated neurotoxicity suggest an etiologic role for altered porphyrin synthesis in lead neurotoxicity.