SERVQUAL is a multi-dimensional research instrument, designed to capture consumer expectations and perceptions of a service along the five dimensions that are believed to represent service quality. SERVQUAL is built on the expectancy-disconfirmation paradigm, which in simple terms means that service quality is understood as the extent to which consumers' pre-consumption expectations of quality are confirmed or disconfirmed by their actual perceptions of the service experience. When the SERVQUAL questionnaire was first published in 1985 by a team of academic researchers, A. Parasuraman, Valarie Zeithaml and Leonard L. Berry to measure quality in the service sector, it represented a breakthrough in the measurement methods used for service quality research. The diagnostic value of the instrument is supported by the model of service quality which forms the conceptual framework for the development of the scale (i.e. instrument or questionnaire). The instrument has been widely applied in a variety of contexts and cultural settings and found to be relatively robust. It has become the dominant measurement scale in the area of service quality. In spite of the long-standing interest in SERVQUAL and its myriad of context-specific applications, it has attracted some criticism from researchers.

The instrument which was developed over a five-year period; was tested, pre-tested and refined before appearing in its final form. The instrument's developers, Parasuman, Ziethaml and Berry, claim that it is a highly reliable and valid instrument. Certainly, it has been widely used and adapted in service quality research for numerous industries and various geographic regions. In application, many researchers are forced to make minor modifications to the instrument as necessary for context-specific applications. Some researchers label their revised instruments with innovative titles such as EDUQUAL (educational context), HEALTHQUAL (hospital context) and ARTSQUAL (art museum).

The model of service quality, popularly known as the gaps model was developed by a group of American authors, A. Parasuraman, Valarie A. Zeithaml and Len Berry, in a systematic research program carried out between 1983 and 1988. The model identifies the principal dimensions (or components) of service quality; proposes a scale for measuring service quality (SERVQUAL) and suggests possible causes of service quality problems. The model's developers originally identified ten dimensions of service quality, but after testing and retesting, some of the dimensions were found to be autocorrelated and the total number of dimensions was reduced to five, namely - reliability, assurance, tangibles, empathy and responsiveness. These five dimensions are thought to represent the dimensions of service quality across a range of industries and settings. Among students of marketing, the mnemonic, RATER, an acronym formed from the first letter of each of the five dimensions is often used as an aid to recall.

Further testing suggested that some of the ten preliminary dimensions of service quality were closely related or autocorrelated. Thus the ten initial dimensions were reduced and the labels amended to accurately reflect the revised dimensions. By the early 1990s, the authors had refined the model to five factors which in testing, appear to be relatively stable and robust.

Construct validity: The model's developers tested and retested the SERVQUAL scale for reliability and validity. However, at the same time, the model's developers recommended that applied use of the instrument should modify or adapt them for specific contexts. Any attempt to adapt or modify the scale will have implications for the validity of items with implications for the validity of the dimensions of reliability, assurance, tangibles, empathy and responsiveness.

Operational definition of the expectations construct: The way that expectations has been operationalised also represents a concern for theorists investigating the validity of the gaps model. The literature identifies different types of expectations. Of these, there is an argument that only forecast expectations are true expectations. Yet, the SERVQUAL instrument appears to elicit ideal expectations. Note the wording in the questionnaire in the preceding figure which grounds respondents in their expectations of what excellent companies will do. Subtle use of words can elicit different types of expectations. Capturing true expectations is important because it has implications for service quality scores. When researchers elicit ideal expectations, overall service quality scores are likely to be lower, making it much more difficult for marketers to deliver on those expectations.

Administration of the questionnaire: Some analysts have pointed out that the SERVPERF instrument, developed by Cronin and Taylor, and which reduced the number of questionnaire items by half (22 perceptions items only), achieves results that correlate well with SERVQUAL, with no reduction in diagnostic power, improved data accuracy through reductions in respondent boredom and fatigue and savings in the form of reduced administration costs.

In spite of these criticisms, the SERVQUAL instrument, or any one of its variants (i.e. modified forms), dominates current research into service quality. In a review of more than 40 articles that made use of SERVQUAL, a team of researchers found that few researchers concern themselves with the validation of the measuring tool. SERVQUAL is not only the subject of academic papers, but it is also widely used by industry practitioners.