A study of 3,021 people in Munich looked at the incidence of social anxiety disorder and depression and examined the possible links between the two conditions. The ten-year study found that 11% of people suffered from social anxiety at some point with the peak age for the condition being between 10 and 19. 27% of people suffered from depression over the ten-year period although this tended to occur at an older age. Social anxiety disorder led to an increased risk of depression in later life.
Beesdo, Katja - Incidence of social anxiety disorder and the consistent risk for secondary depression in the first three decades of life Archives of General Psychiatry August 2007, 64(8), 903-912