All studies in this thesis are cross-sectional and based on self-report questionnaires. Each variable is only measured on one occasion for each participant. Cross-sectional designs are useful for identifying correlates and associated features. They are well suited when studying conditions or characteristics of individuals, such as for example physical self-concept and values in different age groups. However, causal relations cannot be directly demonstrated, and sampling biases may occur, depending on how the cases are identified (Kazdin, 2003). These designs however, can determine the type of association as well as the strength of the
association between two or more variables. Furthermore, the extent to which this association is affected by controlling other variables can also be assessed (Howitt & Cramer, 2005). By using such a design it is possible to examine gender differences (Study II, III, IV) and also to test the factor structure of an existing instrument (Study I).
Study I and Study II
Participants
In spring 2001, students in all 53 elementary- and secondary-schools in Trondheim, Norway were invited to participate in a study about physical self-concept. At the time of data
collection, the majority of citizens in Trondheim were white Norwegians. As Trondheim is a university city, schools are very often asked to participate in different research projects. This means that some schools were already included in other research project when they received invitation about the present study. As a result we knew it could be quite challenging to include a very large number of schools in the project. Thus, to ensure an acceptable number of
participants, it was a major point to start out with a large number of schools. Many things may have influenced the principals’ decision about participation, such as his or her opinion about the importance of this actual project. Also, the fact that the school was busy within other research project or otherwise preoccupied at that specific point in time. Lack of parental consent or students being absent when the questionnaire was administered has of course also influenced the number of participants.
A number of 11 schools were positive to participate, and a total of 1233 students from 5th – 10th grade were asked to fill in a self-report form. Out of these, 1098 (89%) returned completed forms. Missing data is likely to have a more dramatic effect on student level than on school level. In the present study missing on student level (11%) is regarded as acceptable.
The schools represent different parts of the city, and they are believed to represent a mean of the population.
Instrument
The Physical Self-Description Questionnaire (PSDQ) (see Appendix I)
The Physical Self-Description Questionnaire (PSDQ) is a 70-item questionnaire that measures nine specific components: Appearance (e.g., “I have a nice looking face,” “I am good
looking”); Strength (e.g., “I am a physically strong person,” “I am stronger than most people my age”); Endurance (e.g., “I can run a long way without stopping,” “I can be physically active for a long period of time without getting tired”); Flexibility (e.g., “My body parts bend and move in most directions well,” “I am quite good at bending, twisting, and turning my body”); Health (e.g., “I hardly ever get sick or ill,” “When I get sick it takes me a long time to get better”); Coordination (e.g., “I feel confident when doing coordinated movements,” “I can perform movements smoothly in most physical activities”); Physical Activity (e.g., “I often do exercise or activities that makes me breathe hard,” “I do lots of sports, dance, gym or other physical activities”); Body Fat (e.g., “I have to much fat on my body,” “My stomach is too big”); and Sports Competence (e.g., “I am good at most sports,” “I have good sports skills”); one Global Physical scale (e.g., “Physically, I am happy with myself,” “I am satisfied with the kind of person I am physically”); and one Global Self-Esteem scale (e.g., “Overall, most things I do turn out well,” “Overall, I am no good”).
Each of the PSDQ sub-scales contains six items except for the Health and Global Self- Esteem subscale that has eight items. Each PSDQ item is a declarative statement, and
participants respond in the original instrument on a six-point true-false scale with the respond alternatives; “false” – “mostly false” – “more false than true” – “more true than false” – “mostly true” – “true.” However, these six-point respond alternatives may be difficult to comprehend for young children. Especially, the two alternatives “more false than true” and “more true than false” may represent a challenge to young children when they shall
distinguish between these two in addition to the other alternatives.
Marsh and his colleagues (1990d, 1984) have successfully used a five response scale with the respond alternatives; “false” – “mostly false” – “sometimes false/sometimes true” – “mostly true” – “true” in their Self-Description Questionniare I upon which the PSDQ is based, and that also focuses on younger children (from grade 2). In SDQ I, the categories “more false than true” and “more true than false” are replaced with the one category “sometimes false/sometimes true.” It is assumed that it will be easier for young children to
comprehend this one category. Based upon this argument, the original six-point scale was reduced to a five-point scale also in the present study because children as young as 10 years of age were included as participants. Furthermore, in the Norwegian PSDQ scale a five-point scale with the respond alternatives; “totally disagree” – “disagree” – “disagree a little/agree a little” – “agree a little” – “totally agree” were used. This change in wording was done because results from a pilot study, carried out in a Norwegian sample, showed that these respond alternatives turned out to be more understandable among Norwegian adolescents compared to the original “true-false” alternatives. Furthermore, idiomatically it fits better with the
Norwegian language, and it is better in understanding with the English semantic meaning of the expressions. By the use of a five-point scale, results from the present study would not be comparable with previous research when comparing mean values. This represents however not a problem when comparing relations between variables. More important than being able to compare mean values is the question about good reliability of an instrument.
The questionnaire was translated into Norwegian by the author of Study I using the version provided by Marsh et al. (1994). Then, a cross-translation was conducted by a researcher who is fluent in both English as well as Norwegian.
Procedure
After granted permission to perform the studies from the schools, teachers helped by sending information letters to parents. The letters briefly explained the purpose of the studies, and consent from parents was deemed necessary before participation in the project. The Physical Self-Description Questionnaire (PSDQ) was administered during class hours. The students were informed about the study and the questionnaire was not a test and there were no right and wrong answers. Participants were assured that their responses would be completely confidential and that they were free to participate and that they could opt out at any point of time. For students who felt that they did not understand the questions, questions were read aloud by one researcher. To take account of possible differences in reading and writing skills, students were given as much time as needed to complete the items.
Statistical analyses
Statistical analyses were carried out by the use of SPSS for Windows, version 12.0.1 and LISREL, version 8.54.
In study I, Confirmatory Factor Analysis (CFA’s) was conducted to test factorial invariance of an 11 dimensional model for PSDQ across age and gender among Norwegian
elementary- and secondary-school students. Factor analysis was performed to examine the factor structure in the Norwegian sample.
In study II, univariate statistical analyses on scales and sums of scales were performed. T-test was conducted to detect gender differences in multidimensional physical self-concept. Two-way ANOVAs were used to assess the main effects of age and gender, as well as possible age by gender interactions across the nine subdomains of physical self-concept and the Global Physical and Global Self-Esteem scales. To ascertain the effect of the various independent variables on Global Self-Esteem, multiple regression procedure was used.