Organizers of the informatics contest Bebras in many countries face the obstacle of how to state the difficulty of contest tasks and problems accurately. This is essential if tasks with good prediction of success are to be selected for the contest.
The paper discusses five different indicators of a contest task difficulty. We study which of the indicators are correlated. Index of task difficulty was defined as a combination of indicators with the aim of pinpointing the factors that have impact on a contest task difficulty. The index has been constructed on the basis of calculations from some of these indicators.
Using statistical analysis of data from Czech Beaver of Informatics contest we try to assess if some of the proposed factors can be reliable indicators of whether a task is more or less difficult. The findings show that there is a provable link between a task difficulty and the use of formalized description of the task, structuring, optimization, task assignment reading comprehension difficulty and interactivity of answers. The findings of this research study will be useful for organizers of informatics contests as well as school curricula developers.