The evaluation of batch experimental of data from laboratory and pilot testwork e.g. batch leaching of metal from sulphide ores, may be utilised to determine the optimum process conditions. Statistical analysis techniques should allow for the rime-dependent nature of the data as failure to recognise and correct for such rime dependency may lead to incorrect interpretation of the data. This paper illustrates a corrective technique for time-dependent batch data. The technique is demonstrated using a typical data set from a batch bioleach experiment.