“At Microsoft, we strive to ensure that our certifications are relevant, respected, and highly valued within the IT community and that they objectively prove the expertise of technology practitioners. Earning a Microsoft Certification helps demonstrate an individual's comprehension of the latest IT developments and mastery of skills in a specific technology. Microsoft Certifications command great respect in the industry, thanks in part to the thorough and meticulous process used to develop the exams.” Microsoft Certification Exam Development site.
From a statistical perspective, the certification team uses methods approved by the certification industry. You may have noticed that there is a trend for everyone doctors, mechanics, engineers, computer professionals to get certified within their respective industries. The exam development team, in conjunction with a psychometrician, rely on statistics to help ensure that the exam is statistically reliable, questions are at the right level of difficulty (questions that are too easy/too difficult do not contribute to your passing score), and the passing mark is set at the right difficulty level.