Gap scores are computed and the attributes are then ordered by the size of their gap scores. A t-test can be used to determine where statistical significance lies among gap scores. The magnitude of an attribute's gap score should not change significantly over time. The relationship between a service quality attribute and overall satisfaction with transit service can be assumed to be structural. That is, once it is determined that an attribute is a driver of customer satisfaction it will probably remain so, unless significant societal changes occur, i.e., graffiti comes to be viewed as an art form.