def get_analysis_type(self, instance):
        """Returns the string used in slots to differentiate amongst analysis
        types
        """
        if IDuplicateAnalysis.providedBy(instance):
            return 'd'
        elif IReferenceAnalysis.providedBy(instance):
            return instance.getReferenceType()
        elif IRoutineAnalysis.providedBy(instance):
            return 'a'
        return None
Returns the string used in slots to differentiate amongst analysis
        types