Human-computer interaction (HCI) researchers and practitioners have explored how computers and software can aid users in decision-making. Accurate information is crucial in decision-making; therefore, when designing a management information system (MIS), it is necessary to understand the information needs of the end-users and to incorporate this understanding in a way which allows the users to obtain an accurate and intuitive snapshot of the data. Although most of the day-to-day decisions in various organisations are made by middle management employees (as opposed to executives and senior managers), previous literature has scarcely examined how middle management employees' decision-making process can be improved through the use of MIS. In this study, we examine the impact of different data summarisation and visualisation layouts on different aspects of the decision-making process taking into consideration the decision-makers' personal characteristics, and propose to include the results of this examination in the MIS design. To this end, we recruited participants from a crowdsourcing platform. Participants were required to complete a task which simulates middle management employees' day-to-day operational decision-making scenario. To better understand the effects of participants' personal characteristics and their visual abilities, participants were asked to answer a personality questionnaire and a questionnaire testing for visual abilities. The results indicate that when looking at the population as a single group, the effect of the data summarisation and visualisation layouts on the decision-making process cannot be discerned. However, when taking into consideration additional user characteristics, the results indicate that the data summarisation and visualisation layouts affect the decisions made.