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Br J Clin Pharmacol. 1989 Dec;28(6):647-53.

Testing for bimodality in frequency distributions of data suggesting polymorphisms of drug metabolism--histograms and probit plots.

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University Department of Pharmacology and Therapeutics, Royal Hallamshire Hospital, Sheffield.


1. The shape of histograms used to illustrate density distributions of indices of polymorphic drug metabolism was shown to be sensitive to the position of the cell divisions. 2. Non-linearity of the probit plot was shown not to indicate bimodality of the original density distribution. Computer simulation was used to generate examples of unimodal density distributions with curvilinear probit plots. 3. Using the same technique probit plots for bimodal density distributions were constructed. Some were shown to differ less from the probit plots of certain unimodal distributions than did the original density distributions. 4. The position of the antimode was shown not to coincide with inflections seen in the probit plots. 5. A new method for determining the linearity of probit plots is suggested.

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