This paper presents an alternative way of assessing equality of opportunity, called opportunity bias, and compares it with the standard approach. We consider that society is partitioned in a collection of types, consisting of population subgroups that gather people with similar circumstances. Opportunity bias refers to the differences between the outcomes distributions of the different types. We compare those distributions with a method that is valid for evaluation problems involving categorical variables (the balanced worth). An application to the analysis of equality of opportunity in educational achievements, according to PISA, is provided in order to illustrate this approach.