Root-cause analysis is a process of systemic problem-solving that seeks to identify the basic underlying causes that lead to accidents, mistakes and other adverse events. The underlying root cause is determined by looking at the chain of events leading up to the accident. Root-cause analysis can be used in any field in which mistakes can be made, but it's extensively used in the medical field because of the potential severity of adverse results there. In root-cause analysis, the direct cause is that which usually leads immediately to the adverse effect, without any intervening events.
If a person misses an appointment because his car would not start, then the car's failure to start would be the direct cause of his being late, even though there may have been any number of underlying causes for that failure. It is necessary to identify the direct cause of an error to prevent or limit its reoccurrence, but it is important to realize that there are probably other more important contributing factors that led to the direct cause.
Finding a direct cause of an error is usually simple and obvious, but if there were other factors leading to the cause, then attempting to fix the direct cause alone will probably not solve the problem. In the example mentioned above, replacing or recharging the battery may be a temporary fix, but it will not be a long-term solution if you have problems with the alternator. Solutions are more likely to be effective if they address the underlying causes as well as the direct cause.
Direct and root causes occur in many situations. In hospitals, medication errors may result when a nurse misreads the patient's armband. The misreading would be the direct cause of the error, but there are likely other underlying causes that led to the misreading, such as poorly printed armbands, understaffing or nurse fatigue. The direct cause of the Space Shuttle Challenger disaster in 1986 was hot gases escaping from a breach in the solid rocket booster, but the underlying cause was that the O-rings were not designed to function in freezing weather.
Direct causes do not determine the ultimate solutions to most problems. Finding the direct cause is still important, however. Usually, the underlying causes can only be determined by looking at the direct causes first, and the success of any corrective strategy relies on continued monitoring for a reoccurrence of the direct cause. Finally, sometimes the direct causes still have to be remedied, even if they do have an underlying root cause.