Page 94 - Balancing between the present and the past
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                                Chapter 4
source of error. A G-study provides estimates of the variance contributed by persons, observers, occasions of measurement, and each of the possible interactions between these facets. Generalizability theory distinguishes a decision study (D-study) from a G-study. A D-study uses information from a G-study to construct a scoring design that minimizes error for a particular purpose (Shavelson & Webb, 1991). In addition to a G-study, a D-study can identify the optimal data collection for a desired score reliability (Hill et al., 2012).
4.4.4 Sample and data collection
Non-probability sampling was used to select five teachers to observe and five observers (see Tables 11 and 12 for the teachers’ and observers’ characteristics). In the Netherlands, the average age of male teachers is 46 years and that of female teachers is 42 years. The gender distribution of the teachers was 48% female and 52% male. In total, there are 1785 history teachers with a Master’s degree and 3944 history teachers with a bachelor’s degree working in the Netherlands (Dutch Ministry of Education, Culture, and Science, 2011). The teachers in the sample worked at different schools, and these schools did not differ significantly from the total population in regards to student enrollment, location (rural or urban), or graduation rate (Statistics Netherlands, 2014). The national students’ mean score on the formal history exam for general secondary education and pre-university education was 6.35 on a 10-point scale.
Table 11. Teachers’ characteristics
A Male 60
B Male 34
C Male 43
D Male 63
E Male 41
Bachelors 37 Dutch Masters 8 Dutch Masters 17 Dutch Masters 41 Dutch Masters 14 Dutch
Modern History =
Modern History > Early Modern History > Middle Ages > Early Modern History >
          Note. *Students’ mean score on the formal history exam compared to the national mean score on the formal history exam.
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Students’ performance*
Historical expertise
Nationality
Years’ work experience
Educational qualification
Age Gender
Teacher













































































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