Subject Selection and Stratification

 

Statped Vest is a national pedagogical institution serving the four counties of Western Norway. The administrative leader of the logopedics department selected the municipalities of Haugesund (Rogaland County), Kvinnherad (Hordaland county), Førde (Sogn og Fjordane county) and Fræna (Møre og Romsdal county) for participation in the study. In addition, Osterøy (Hordaland county) served as a control municipality. The selection covers two rural and two urban districts, as well as the two Norwegian official orthographies, bokmål (one urban, one rural) and nynorsk (one urban, one rural). 

All school administrations agreed to participate in the study. Due to their local knowledge, the leaders of the pedagogical-psychological services (PPT)  in the municipalities were asked to select the pre-schools where the project would be initiated. 
A total of 120 children across the selected nine preschools were born in 1998. The estimated prevalence of reading and writing impairments is about 5 to 10 %. However, it was expected that a larger percentage would show at-risk signs of dyslexia, but that dyslexia would not develop in all at-risk children. 25 – 30 (21 – 25%) children were expected to represent the at-risk group.
The fifth municipality representing a control group was served with the conventional treatment/follow-up offered by the PPT. This municipality has 95 children born in 1998, and the PPT-service reported 18 (19%) children being referred to their services, mostly due to language and behavioural problems. 
The procedures for identification of the at-risk and control groups are described below.
Step 1: InformationParents of all the 120 children received oral and written information in locally held meetings about the project, and were asked to sign a form of informed consent. The parents were invited to have their children participate in the project, however clearly stating that only some of the children would be offered a special treatment/follow-up. 109 parents answered the questionnaire and agreed to take part in the selection procedure and, if selected, the longitudinal, experimental part of the project. 
Step 2: Questionnaire to Parents and TeachersTo find at-risk children, information about the subjects was collected through questionnaires to parents and pre-school directors. The questionnaire was prepared in accordance with three guiding principles: 

it should cover the main theories of dyslexia, including questions on somatics, language development, motor control and heredity;it should mirror the process of taking the case history before dyslexia assessment;the questions should be easily readable and in a non-professional language, to ensure that they would be read, understood and responded to even by parents who were themselves dyslexic.
Furthermore, information from the parents, PPT and the pre-schools, would be used if needed. Only children with Norwegian as a first language were included. Exclusion criteria were mental retardation (DSM-IV, 1994) and signs/diagnoses of any other impairments (ADHD, various syndroms, neurological impairments, impairments in sight or hearing).             Step 3: Establishing the Experimental Groups. Based on the questionnaires, a risk index was calculated for each child. The mean at-risk score was 9.96% (range 0 – 47.5). Based on this, the at-risk and control groups were established as follows: Tentatively, the upper 25th percentile was used as a cut-off point for the at-risk group. This resulted in a skewed gender profile, with few girls. In order to investigate endophenotypical gender differences, however, the distribution of boys and girls should be more even. Consequently, two at-risk indices were used;

For the boys, the upper 25th percentile of the whole group of 5 year olds was selected, with the cut-off point at 12.49 (range 12.5 – 47.5).For the girls, the upper 25th percentile for the girls only was selected, giving a cut-off point at 9.71 (range 9.72 – 46.90).
This procedure gave an at-risk group of 25 children, 13 boys and 12 girls. Subsequently, a control group of 27 children matched on gender and age (nearest month) was established among the other children. 
There was a significant difference between the two at-risk groups and their respective control groups (1-way ANOVA: F (3,48) = 28.089, p<.00). The Tukey HSD test showed no significant differences between the genders within each group, but significant gender differences between the groups (p<.001 for both genders). Five children were excluded from the list of 109 subjects due to meeting exclusion criteria. 
It should be noted that the PPT, the parents and the schools were encouraged to include children who were excluded in the assessments and interventions although they would not be included in the research project. By project end in 2007 three children from the control group had been taken out of the project. Thus, the data analyses from the first three phases contain data from 49 children, 25 at-risk and 24 controls, see Table 1 for detailed descriptive statistics. In the follow-up phase in 2009/10, 42 children and their parents agreed to take part.  
The WPPSI (Wechsler, 1999) was used as baseline at the initial assessment when the children were five years old (pre-schoolers). Divided by groups (control vs. at-risk) and gender, no significant differences were seen.

Descriptive data