Comparing researches on selective mutism in Japan with that in Western countries, I found that there are differences in age of onset. Reported average age of onset in Japan is higher than that in Western countries. In Japan, average age of onset is about 5 years old. On the other hand, in Western countries, average age of onset is about 3 years old.
There are a small number of researches that report age of onset, so it may be premature to conclude that Japanese children with selective mutism show their symptoms later. But I'm curious about the difference.
[The average age of onset of SM and SM literature]
Here are major researches that report the age of onset of selective mutism. Regrettably, I can't collect all reports.
I write the average and standard deviation of age of onset here as possible. But some researches doesn't report them. In that case, I calculate them. And in some cases, the age of onset are reported to be a-b years. (e.g. 3-5 years). In that case, I regard it a+b/2 years (e.g. 4 years).
[Points keep in mind when comparing the age of onset]
* Diagnostic criteria
There are many studies on selective mutism, but old researches, especially Japanese ones, tend to use various diagnostic criteria. On the other hand, recent researches, especially Western ones, tend to use standardized diagnostic criteria, such as DSM and ICD. So, it is difficult to make a simple comparison of them.
* Subjects
The average age of onset depend on subjects. For instance, like Elizur et al. (2003), the average age of onset can't be old if children were recruited from preschools. On the other hand, like Minami et al. (1987) or Ichitani et al. (1973), the average age of onset can be older if children were recruited from child consultation centers which aim at children under 18 years.
[SM literature in Japan]
* Shiina et al., 1998
The average age of onset is 4.9 years. 38 out of 46 cases presented symptoms from 2 to 7 years. The data is based on case studies published from 1980 to 1996.
* Souma, 1991
25 out of 35 cases presented symptoms before they enroll in elementary school. The data is based on case studies published from 1980 to 1989.
* Minami et al., 1987
The average age of onset is 5.0 and standard deviation is 2.3 except 2 unclear cases. 28 cases showed their symptoms first in their childhood (3-5 years). 3 cases showed their symptoms first when they were in elementary school (6-11 years). 2 cases showed their symptoms first at puberty (after age 12). 1 case was unclear. The data is based on patients who receive medical consultation at Kyoto City child consultation center from fiscal 1960 to 1987.
* Muramoto, 1983
Out of 17 cases, the average age of onset is 6.4 years and standard deviation is 2.8 years. 3 cases were 3 years. 2 cases were 4 years. 2 cases were 5 years. 3 cases were 6 years. 2 cases were 7 years. 1 case were 8 years. 1 case was 11 years. 1 case was 13 years. The data is based on questionnaire survey conducted at public elementary and junior high schools in Kamikawa, Hokkaido, northern Japan.
* Oi et al., 1979
Out of 24 cases, the average age of onset is 3.8 years and standard deviation is 0.8 years except 1 unclear case. 9 cases were 3 years. 10 cases were 4 years. 3 cases were 5 years. 1 case was 6 years. The data is based on patients Oi was related to intensively at child psychiatry clinic at Nagoya University and Kusunoki Gakuen, a residential treatment center for emotionally disturbed children.
* Araki, 1979
Out of 34 cases, the average age of onset is 5.9 years and standard deviation is 2.2 years. 1 case was 2 years. 2 cases were 3 years. 6 cases were 4 years. 7 cases were 5 years. 11 cases were 6 years. 1 case was 7-8 years. 6 cases were 9-11 years. The data is based on patients who visited department of psychiatry at Kyushu University from 1963 to 1976.
* Ichitani et al., 1973
Out of 20 cases, the average age of onset is 5.4 years and standard deviation is 1.6 except 1 unclear case. 10 patients showed symptoms first when they started kindergartens or nursery schools. 5 patients showed symptoms first when they entered elementary schools. 4 patients showed symptoms first a few years after they entered elementary schools. 1 patient was unclear. The data is based on 20 elementary school students who visited Osaka City and Kyoto City child consultation centers and were diagnosed as selective mutism from May 1964 to December 1970.
[SM literature in Western countries (written in English)]
* Cunningham et al., 2004
Out of 52 cases, the average age of onset is 3.3 years. The age of onset ranged from 3 to 5. Children were diagnosed according to DSM-IV criteria. They were recruited over a period of 9 years from a regional service providing child assessments, school consultations, and workshops for parents and teachers.
* Elizuret et al., 2003
Out of 19 cases, the average age of onset was 3 years and 4 months. Onset was significantly earlier among native children (2.7 years) versus immigrant children (3.9 years). Children were recruited from West Jerusalem's obligatory and pre-obligatory state preschools. and diagnosed according to DSM-IV criteria.
* Remschmid et al., 2001
In 43 out of 45 cases, the first age of manifestation was three years. Only in two cases take, the first manifestation did place later. Children had been referred between 1964 and 1979 to the Department of Child and Adolescent Psychiatry (impatient and outpatient unit) and to the Child Guidance Clinic which works closely together with the department. They were diagnosed according to DSM-III-R criteria.
* Kristensen, 2000
Out of 54 cases, the average age of onset is 3.7 years and standard deviation is 1.7 years. Children were diagnosed according to DSM-IV criteria, but exclusion criteria for SM on Asperger's disorder and communication disorder were ignored to look for comorbidity. Children were recruited by mailing announcements to all 63 outpatient clinics for child and adolescent psychiatry and all 278 school psychology services in Norway.
* Dummit et al., 1997
Out of 54 cases, the average age of onset is 3.4 years and standard deviation is 1.3 years. Children were diagnosed according to DSM-IV criteria. They were recruited through advertising and referral from local schools and the Selective Mutism Foundation.
* Steinhausen et al., 1996
Out of 100 cases, the average age of onset is 49.5 months and standard deviation is 32.5 months. In the SHG sample, the average age of onset is 43.9 months and standard deviation is 26.3 months. In the ZH sample, the average age of onset is 45.8 months and standard deviation is 25.5 months. In the B sample, the average age of onset is 63.9 months and standard deviation is 52.4 months. Children were diagnosed according to ICD-10 criteria.
SHG sample (n = 19) was personally assessed by the senior author in 1992 and 1993 because of personal contacts with a parents' self-help group that had been formed in the German-speaking cantons of Switzerland. ZH sample (n = 59) was seen between 1979 and 1992 in the Child and Adolescent Psychiatric Service of Canton of Zurich. B sample (n = 22) represents the entire group of electively mute children who were identified in the case files of the Department of Child and Adolescent Psychiatry at the Free University of Berlin.
* Black et al., 1995
Out of 30 cases, the average age of onset is 2.7 years and standard deviation is 1.4 years (range: 1 through 5 years). All children satisfied the diagnostic criteria for both DSM-III-R and DSM-IV.
* Black et al., 1981
unclear.
* Hayden 1980
Sorry, I dont't understand the age of onset reported in the paper.
* Wergeland, 1979
All patients (n = 11) represented symptoms at 3 - 4 years. The age at which they were referred varied from 6 to 11 years with an average of 9 1/2 years. One of the children was referred by kindergarten staff, the other 10 by the school authorities.
Index of SM in Japan
