Most organizations use forecasting techniques in order to achieve their goals and to reduce risk in uncertain conditions and varying situations. Forecasting by senior managers plays a very important role in the success or failure of organization and company projects as well as their affairs. However, the scope of forecasting has not yet structured or regulated and there is no approved or special conceptual framework for it, especially in relation to the reasons decisions of mangers deviate while forecasting, which can have a crucial influence on the whole organization. The aim of this study is to develop a conceptual model of the reasons for deviation from forecasting by senior managers. To understand the subject, a systematic review and meta-analysis of the research and literature was carried out. A conceptual model was developed according to the results of this research and the data from a focus group. The results of meta-analysis show that trends in optimistic and pessimistic forecasting and senior managers are the main reasons for deviations from forecasting by management. Moreover, it did not confirm that voluntary forecasts are responsible for increased accuracy in forecasting by management, and that there are still contradictions in this field. The results of our meta-analysis also indicated that some studies considered voluntary disclosure of forecasting as a factor in the reliability of the forecasting. Some researchers consider it as a factor of an optimistic trend of forecasting and others consider it as a factor effecting deviation from forecasting by management directly due to the individual motivation of managers and inaccuracy of information on which the decisions are made. According to the findings, it was not confirmed that voluntary forecasting on its own is a factor in the accuracy of forecasting
