5. What service variables are drivers of financial performance in each tier? One of the most fascinating issues in this category is whether service drivers are the same in different service tiers. The single academic study to date (Zeithaml et al. 1999) suggests that they are not. Customers in two different tiers view quality differently. For the top tier, a factor called speed (which involved how quickly the customer was served) was key to driving incidences of new business, while for the lower tier, a factor called attitude (involving the way the customer was treated by employees) was the driver. Analysis showed that combining the two tiers would result in a muddied picture that would identify drivers unlikely to satisfy either tier.