The lifetime prevalence, or the proportion of individuals expected to stutter at one time in their lives, is about 5%, and overall males are affected two to five times more often than females. However, there is not much information known about the underlying cause for such a skewed sex ratio. Most stuttering begins in early childhood, and studies suggest that 2.5% of children under the age of 5 stutter. As seen in children who have just begun stuttering, there is an equivalent number of boys and girls who stutter. Still, the sex ratio appears to widen as children grow: among preschoolers, boys who stutter outnumber girls who stutter by about a two to one ratio, or less. This ratio widens to three to one during first grade, and five to one during fifth grade, as girls have higher recovery rates. Due to high (approximately 65–75%) rates of early recovery, the overall prevalence of stuttering is generally considered to be approximately 1%.