5. CONCLUSION
Service quality is the best tool for marketing managers to find and analyze information about customer needs, wants, and perceptions about services. This information will help managers to identify problems and make strategic plans in order to improve efficiency, profitability, and overall performance by high quality. During recent decades, scientists attempted to find the perfect model in measuring service quality that cover all the factors and answer to this area of necessity. There are many models suggested by researchers and all models have their own advantages and disadvantages. Scientists are not unanimous about any of these service quality models. Service quality models have different dimensions regarding the field of service sectors. However, SERVQUAL is the most common model used by researchers but it is not comprehensive and suitable for different applications. The hierarchical model has covered weaknesses of other models. It has strong structure and specifies the factors of customer perspective as well. Moreover, Hierarchical measurement considers services outcomes, which were void in SERVQUAL. Validity and Reliability of this model has been tested and approved in different areas by other marketing researchers. Results show the hierarchical instrument as the most advantageous approach to service quality assessment to date (Pollack, 2009) . Finally, by this review of literature we can conclude that the Hierarchical Service Quality is the most suitable and helpful measurement for managers to collect the right information and make the right decisions.