An accident is an unintended, normally unwanted event that was not directly caused by humans. The term accident implies that nobody should be blamed, but the event may have been caused by unrecognized or unaddressed risks. Most researchers who study unintentional injury avoid using the term accident and focus on factors that increase risk of severe injury and that reduce injury incidence and severity. For example, when a tree falls down during a wind storm, its fall may not have been caused by humans, but the tree's type, size, health, location, or improper maintenance may have contributed to the result. Most car wrecks are not true accidents; however, English speakers started using that word in the mid-20th century as a result of media manipulation by the US automobile industry.