An evaluation of the methods available for analysing results from migration inhibitory factor (MIF) test.

In order to illustrate the potential dangers in using some of the methods available for calculating migration inhibitory factor (MIF) activity, selected results have been analysed in a number of different ways. The weights corresponding to the migration areas were used in a single ratio expression and then in a double ratio formula to calculate migration inhibition. Conclusions from these results were made using both the arbitrary 20% inhibition to indicate MIF activity and a statistically-derived minimum percentage inhibition needed to demonstrate a significant effect. The procedure was then repeated using the square root of the weight equivalents of the migration areas. A double ratio expression was preferable to the single ratio formula as the former considered the information from all the control cultures. The degree of inhibition needed to demonstrate MIF activity varied between tests and for accurate interpretation of the results it was necessary to use a statistically derived minimum value for inhibition in each experiment. Use of the square root of the weight equivalents of migration areas in the double ratio method gave conclusions analogous to those using the actual weights. Use of the square root transformation narrowed the difference between sample means and caused a corresponding reduction in within-sample variability.