What causes problems in planning? The influence of task characteristics onthe difficulty of scheduling

In each of two identically-structured scheduling tasks, the influence of "c omplexity" (4, 8, 12 activities to bring into an optimal sequence) as well as "time" (adding vs. leaving out of either fixed times or periods of time) on the objective (required time, errors) and the perceived difficulty were explored. Additional interest is in the influence of content-effects of id entically-structured tasks which differ in their semantic embedding. In both tasks the perceived and the objective difficulty increased (increas ing required time, declining quality of solution) with the complexity. Addi tional fixed times lower, while additional periods of time heighten the dif ficulty. The variation of the semantic embedding has a significant influenc e on the required time and the perceived difficulty. At high perceived diff iculty, external planning activities are more often executed.