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<unk>  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<unk> , 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<unk>  is generally considered to be approximately 1%. Cross-cultural studies of<unk>  prevalence were very active in early and mid-20th century, particularly under the influence of the works of Wendell Johnson, who claimed that the onset of<unk>  was connected to the cultural expectations and the pressure put on young children by anxious parents. Johnson claimed there were cultures where<unk> , and even the word "stutterer", were absent (for example, among some tribes of American Indians). Later studies found that this claim was not supported by the facts, so the influence of cultural factors in<unk>  research declined. It is generally accepted by contemporary scholars that<unk>  is present in every culture and in every race, although the attitude towards the actual prevalence differs. Some believe<unk>  occurs in all cultures and races at similar rates, about 1% of general population (and is about 5% among young children) all around the world. A US-based study indicated that there were no racial or ethnic differences in the incidence of<unk>  in preschool children. At the same time, there are cross-cultural studies indicating that the difference between cultures may exist. For example, summarizing prevalence studies, E. Cooper and C. Cooper conclude: "On the basis of the data currently available, it appears the prevalence of fluency disorders varies among the cultures of the world, with some indications that the prevalence of fluency disorders labeled as<unk>  is higher among black populations than white or Asian populations" (Cooper & Cooper, 1993:197). In his<unk>  and its Treatment: Eleven lectures" Mark Onslow remarked that "one recent study with many participants (N=119,367) convincingly reported more<unk>  among African Americans than other Americans. Why this could be the case is challenging to explain..." Different regions of the world are researched very unevenly. The largest number of studies has been conducted in European countries and in North America, where the experts agree on the mean estimate to be about 1% of the general population (Bloodtein, 1995. A Handbook on<unk> . African populations, particularly from West Africa, might have the highest<unk>  prevalence in the world—reaching in some populations 5%, 6% and even over 9%. Many regions of the world are not researched sufficiently, and for some major regions there are no prevalence studies at all (for example, in China). Some claim the reason for this might be a lower incidence in the general population in China.
Stuttering
Hoarse voice
Drooling
Spasmodic dysphonia
Stilted speech
Facial toning
Kussmaul breathing
Sleepwalking