About 12% of people are affected by an anxiety disorder in a given year, and between 5% and 30% are affected over a lifetime. They occur in females about twice as often as in males and generally begin before age 25. The most common are specific phobias, which affect nearly 12%, and social anxiety disorder, which affects 10%. Phobias mainly affect people between the ages of 15 and 35, and become less common after age 55. Rates appear to be higher in the United States and Europe than in other parts of the world.