In diverse industrial and academic environments, the quality of the software has been evaluated (validated) using different analytic studies. It is a common practice on these environments, the use statistical models for the assurance, control and evaluation of the quality of a software product or process. A number of industries in the safety-critical sector are forced nowadays to use such processes by industry-specific standards (e.g., the DO-178B standard for airborne software systems). The contribution of the present work is focused on the development of a methodology for the evaluation and analysis of the reliability of web-based software applications. We tested our methodology in a web-based software system and used statistical modeling theory for the analysis and evaluation of the reliability. The behavior of the system under ideal conditions was evaluated and compared against the operation of the system executing under real conditions. The Personal Software Process (PSP) was introduced in our methodology for improving the quality of the process and the product. The Evaluation + Improvement (Ei) process is performed in our methodology to evaluate and improve the quality of the software system. The results obtained demonstrated the effectiveness and applicability of our methodology.