Environment factor, private information and the controllability principle

Should a manager be held accountable for uncontrollable environment factors like foreign exchange rate or oil price? To address this question, we develop a multi-task agency model where the agent has a limited liability. The profit of the firm is impacted by a stochastic environmental factor which changes the relative productivity of tasks, and whose realization is public ex-post. The agent-manager observes an early private signal of the environment and thus knows better than the principal which task it is optimal to undertake. For the principal, there is therefore a trade-off between congruity (induce the agent to use her information as the principal would use it) and agency costs (in particular to induce the agent to reveal this information).In our model, it is costly to make the agent responsible for the environment, not because the environment is uncertain, but because the agent has a better knowledge of the environment when the task is chosen. The optimal contract depends on the informativeness of the signal. For an highly informative signal the environment is not filtered from the performance measure to encourage a congruent action from the agent. For a poorly informative one, the environmentis eliminated and the agent never reacts to it: congruity is given up to decrease the agency cost. We use this model to discuss the application of the controllability principle in the case of external environment factor.