Step One is to determine which attributes have the most impact on overall customer satisfaction. For each attribute, the sample is divided into those respondents who have had a recent problem with the attribute and those respondents who have not recently experienced a problem with the attribute. (Those who have not experienced the attribute within the past 30 days are grouped with those who have, but have not had a problem.) The mean overall satisfaction ratings of the two groups are compared. The difference between the two mean overall satisfaction ratings is called the "gap score". 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.