Nowadays according to the intention of many hospitals and medical centers to computerize their processes and medical treatments including data forms and medical images which are generating a huge amount of data, IT specialists and data scientists who are oriented to eHealth and related issues know the importance of data integrity and its benefits. This study attempts to indicate the significance of data integrity, especially in medical information systems. It means that the medical sub-systems in HIS (Hospital Information System) must be integrated and it is also necessary to unify with MIS (Management Information System). In this paper accuracy level of the extracted reports from the Information System (to evaluate the staff’s performance) in two ways has been measured: 1- At first, the performance of the clinic reception staff will be evaluated. In this way, the personnel attendance system is an independent and separated software, and the mentioned evaluation has been done by its report. 2- Next year in the same location precisely the same evaluation has been done based on the data extracted from the personnel attendance sub-system which has been added to the medical information system as an integrated information system. After comparing the accuracy level of both ways, this paper concludes that when the personnel attendance sub-system as a part of MIS has been unified with HIS and its sub-systems, how much the reports and consequently management decisions will be more accurate and more reliable and therefore the managers and decision-makers will perceive the importance of data integrity more than the past.