The Zone of Tolerance
Extensive theoretical and empirical work has been conducted in the Marketing discipline
to understand and explain the link between customer satisfaction and service quality. The
greatest volume of research has focused upon the disconfirmation theory, which holds that
satisfaction (dissatisfaction) is dependent upon the size of the confirmation (disconfirmation) of
the service customers’ initial expectations (Churchill and Surprenant 1982). A similar theory,
the Gaps Model of service quality, holds that customer satisfaction is based upon perceptions of
service quality relative to the customer’s initial expectations (Parasuraman, Zeithaml, and Berry
1985). Both perspectives place great emphasis upon the role that expectations serve in the
satisfaction development process.
A refinement of the Gaps Model of service quality is the norms-based zone of tolerance
model, introduced by Zeithaml, Berry and Parasuraman (1993) and further refined by
Parasuraman, Zeithaml, and Berry (1994). The zone of tolerance (ZOT) is defined as “the
difference between desired service and the level of service considered adequate” (Zeithaml et al
1993, pg. 6). As may be noted in this definition, the ZOT model recognizes that customers enter
service encounters with different expectation levels. Desired service is “the level of service the
customer hopes to receive … a blend of what the customer believes can be and should be”
(Zeithaml et al 1993, pg. 6). On the other hand, adequate service is the “level of service the
customer will accept” (Zeithaml et al 1993, pg. 6). The difference between these two
expectation standards is the zone of tolerance. The ZOT model proposes that satisfaction will
result as long as customer perceptions of service performance fall in the zone. Zeithaml and her
colleagues (1993) proposed that the ZOT varies across customers and can expand/contract with
the same customer. They also proposed that adequate service expectations are subject to change,
while desired service expectations are relatively enduring.
Parasuraman et al (1994) continued development of the ZOT model by testing three
alternative questionnaire formats using an extensive mailing of 12,470 questionnaires. A total of
3069 usable questionnaire were returned for a response rate of 25%. Focusing on the five
SERVQUAL dimensions of reliability, responsiveness, assurance, empathy, and tangibles
(Parasuraman, Zeithaml, and Berry 1988), the three column format measured the respondents’
adequate and desired expectations, as well as their perceptions of the service provider’s
performance in identical, side-by-side scales. The two column format generated direct measures
of the service-superiority gap (perceived performance on desired service levels) and the serviceadequacy gap (perceived performance on adequate service levels) with identical, side-by-side
scales. The one column format generated direct measures of both the service-superiority and
service-adequacy gaps, but the questionnaire was split into two parts, with one set of scales
designed to measure each of the gaps separately. Parasuraman et al (1994) found that while each
of the formats were both reliable and valid, only the three column format offered the ability to
determine where perceptions fell relative to the ZOT, the ability to pinpoint ZOT positions, and
reduce the chance for inflated ratings and erroneous inferences.
Another theoretical article regarding the ZOT was offered by Johnston (1995).
Specifically, he theoretically examined the relationship between involvement and the ZOT, as
well as the impact of various service performance outcomes upon the ZOT. In relation to the
impact of involvement, he proposed that the width of the ZOT is “inversely proportional to the
degree of involvement” (Johnston 1995, pg. 49). In other words, high involvement generates a
narrower ZOT, while low involvement generates a wider ZOT. Similar to Zeithaml et al’s
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(1993) contention, he also proposed that (1) performance within the ZOT may go unnoticed by
the customer, (2) performance below the customer’s adequate expectations level (below the
ZOT) will generate dissatisfaction, and (3) performance above the customer’s desired
expectations level (above the ZOT) will generate “delight”, or what Zeithaml et al (1993) termed
a “customer franchise.”
It is appropriate to note that disagreement exists in the services marketing literature as to
whether perceived service quality should be measured using a performance-based framework or
with a standards (or norms)-based framework. Teas and DeCarlo (2004, pg. 272) noted that
“performance-based frameworks specify perceived performance, without any comparative
referents, as the perceived quality concept,” while “standards-based frameworks specify a
relative or comparative performance conceptualization of perceived quality.” In other words,
does a direct measure of perceived service quality offer greater explanatory power than a normsbased comparative measure? Parasuraman et al (1994) argued that norms-based models (such as
the ZOT) would be more useful because of the measurement of more precise information about
customer perceptions across the multiple expectations levels. In their study of 107
undergraduate students’ perceptions of a university’s Student Services Center, Teas and DeCarlo
(2004) found that performance-based models offered more explanatory power than the ZOT
regarding the relationship between perceived quality and purchase intentions. However, they
also found that the ZOT (as the representative norms-based model) offered superior performance
(relative to performance-based models) when evaluating the linkage between perceived quality
and satisfaction. Hence, they provided support for the ZOT as a useful managerial and research
tool for better understanding how customer perceptions of quality impact satisfaction with the
service.
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Additionally, Voss, Parasuraman, and Grewal (1998) argued that there are instances
when a standards-based framework does not provide sufficient explanatory power. Specifically,
in their study of 200 faculty members of a large university, these authors found that the
standards-based framework was only useful when price and performance were consistent. In
other words, they examined how price perceptions impacted the expectations-perceived
performance framework. They found that the more customers were price tolerant, the less
satisfied they were with a high-price/low-quality offering. On the other hand, for those
customers who were initially less price tolerant, satisfaction was greater for the low-price/highquality offering. Yet, in those instances where levels of delivered performance matched the price
level (low-price/low-quality; high-price/high-quality), perceived performance was compared
against prior expectations to determine satisfaction levels.
Additional support for the ZOT model has been provided by Walker and Baker (2000).
These authors proposed that the width of the ZOT varies for essential versus less-essential
service quality components. They also proposed that the ZOT width would be influenced by the
degree of customer experience with the service, as well as the number of competitive alternatives
the customers perceived. They surveyed 205 college students regarding health club membership.
It was found that the width of the ZOT does indeed varying dependent upon the service quality
dimension in question. Specifically, Walker and Baker (2000) found that the ZOT was narrower
for the assurance and reliability dimensions than for the empathy, responsiveness, and tangible
dimensions of service quality. In relation to customer experience levels, it was found that no
significant differences exist between experienced and non-experienced customers on desired
service level expectations. However, the ZOT is narrower for experienced customers “because
they have increasingly demanding adequate expectations” (Walker and Baker 2000, pg. 424).
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Additionally, these authors found no support for the Zeithaml et al (1993) proposition that the
presence of readily available provider alternatives would narrow the ZOT. Walker and Baker
(2000) attributed this finding to the stability of the desired expectations standard.
Another recent study offered similar findings to those reported by Walker and Baker
(2000). Gwynne, Devlin, and Ennew (2000) also investigated the width of the ZOT relative to
the different service quality dimensions and found in their study of 218 students that service
quality dimensions that are perceived as more important enjoy a wider zone of tolerance. Their
results attribute this to higher levels of desired expectations for the most important service
quality dimensions. It was also found that these desired expectations tend to be relatively stable.
Additionally, customers who were more favorably disposed to the provider (generally more
experienced customers) tended to have higher levels of adequate expectations than their less
favorably disposed counterparts, and thus tended to have narrower ZOT’s.
In summary, the Zone of Tolerance (ZOT) model is a standards-based framework for
understanding customer perceptions of service quality and satisfaction with the service. While
the ZOT is inappropriate in some instances, such as when the primary purpose is “to explain the
variance in some dependent construct,” it is considered appropriate when “the primary purpose is
to diagnose accurately service shortfalls” (Zeithaml et al 1996, pg. 40). The model holds that
service customers has two basic types of prepurchase expectations; desired and adequate. These
expectations define the boundary of the zone of tolerance. As long as perceived performance
falls within the zone, the result is customer satisfaction. Performance below the zone generates
dissatisfaction, while high performance that exceeds the customers’ desired expectations
generates delight, or a customer franchise.
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What does the Zone of Tolerance model offer business managers? It explains that the
firm’s customers enter discrete transactions with the organization with different expectations.
They have a level of service they will accept, and they have a level of service they want. As long
as the firm’s offerings fall within the zone, the customers will be satisfied. However, falling
within the zone is only enough to maintain competitive parity. Obviously, falling below the zone
puts the firm at a competitive disadvantage. On the other hand, performing above the zone offers
the firm the possibility of developing a long-term competitive advantage. It is important that the
firm gain an understanding of the service quality dimensions that are most important to its target
customers, for it is within these dimensions that the zone is narrowest. It is likely that
competitive advantage may not be derived from performance on these dimensions, but the firm
must perform within the customers’ zones of tolerance on these dimensions to be competitive.
Yet, the less important dimensions offer an opportunity for the development of sustainable
competitive advantage as the zones of tolerance associated with these dimensions tend to be
wider.
References
Churchill, Gilbert A., Jr. and Carol Surprenant (1982), “An Investigation Into the Determinants
of Customer Satisfaction,” Journal of Marketing Research, XIX (November), 491-504.
Gwynne, Anne L., James F. Devlin, and Christine T. Ennew (2000), “The Zone of Tolerance:
Insights and Influences,” Journal of Marketing Management, 16, 545-564.
Johnston, Robert (1995), “The Zone of Tolerance: Exploring the Relationship Between Service
Transactions and Satisfaction with the Overall Service,” International Journal of Service
Industry Management, 6 (2), 46-61.
Parasuraman, A., Valarie A. Zeithaml, and Leonard L. Berry (1985), “A Conceptual Model of
Service Quality and Implications for Future Research,” Journal of Marketing, 49 (Fall),
41-50.
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Parasuraman, A., Valarie A. Zeithaml, and Leonard L. Berry (1988), “SERQUAL: A MultipleItem Scale for Measuring Consumer Perceptions of Service Quality,” Journal of
Retailing, 64 (Spring), 12-40.
Parasuraman, A., Valarie A. Zeithaml, and Leonard L. Berry (1994), “Alternative Scales for
Measuring Service Quality: A Comparative Assessment Based on Psychometric and
Diagnostic Criteria,” Journal of Retailing, 70 (3), 201-230.
Teas, R. Kenneth and Thomas E. DeCarlo (2004), “An Examination and Extension of the
Zone-of-Tolerance Model,” Journal of Service Research, 6 (February), 272-286.
Voss, Glenn B., A. Parasuraman, and Dhruv Grewal (1998), “The Roles of Price, Performance,
and Expectations in Determining Satisfaction in Service Exchanges,” Journal of
Marketing, 62 (October), 46-61.
Walker, Jim and Julie Baker (2000), “An Exploratory Study of a Multi-Expectation Framework
For Services,” Journal of Services Marketing, 14(5), 411-431.
Zeithaml, Valarie A., Leonard L. Berry, and A. Parasuraman (1993), “The Nature and
Determinants of Customer Expectations of Service,” Journal of the Academy of
Marketing Science, 21 (Winter), 1-12.
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