Regression analysis inappropriate application

Figure 3.2 Example of the inappropriate application of regression analysis to dichotomous activity data (A) as compared to continuous activity data (B). Data distributed as in A are unsuitable for regression analysis because it results in a two-point correlation.

As analytical methods usually have to be applicable over a wide range of concentrations, a new method is often compared with a standard method by analysis of samples in which the analyte concentration may vary over several powers of 10. In this case it is inappropriate to use the paired t-test since its validity rests on the assumption that any errors, either random or systematic, are independent of concentration. Over wide ranges of concentration this assumption may no longer be true. An alternative method in such cases is linear regression (see Section 5.9) but this approach also presents difficulties. 

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