Instrument design
A Health questionnaire on back care knowledge in daily life physical activities (HEBACAKNOW).
To study the level of knowledge on health and back care, an ad hoc four-phase questionnaire was elaborated using a validity criteria based on the Delphi method [
18].
-
Phase I: collecting evidence. Searching for references. Selecting evidence indicators.
-
Phase II: development of version I. Item elaboration. Experts’ evaluation.
-
Phase III: development of version II. Pilot administration. Evaluation by adolescents.
-
Phase IV: development of final version. First administration. Second administration.
To design the questionnaire several sources were considered. First (Phase I), a search for suitable previous work on low back pain, back care, and the use of questionnaires on back care, was made in the specialized literature. We took into account results from studies on basic and applied knowledge to the comprehension of the body mechanics [
20], knowledge on backpack book load [
21], the correct way to carry the backpack [
22], the sitting posture and classroom furniture [
23], and the spine load in different positions [
12,
24].
From this previous research work a first true/false 38-item version of the questionnaire was designed (Phase II). Then, six independent experts (two in medicine and biomechanics, two in physical education and two in educational research methods) were selected. The selection was made according to the following criteria: they should be outside the study, have the PhD or MD grade, work at university and have published a research paper in an impact international journal on back care and health. Experts were asked to judge each item according to: their relevance and suitability for the back care and health in daily life activities, the kind of language used and its adequacy for the sample characteristics. Most of the experts’ suggestions were addressed to the instrument design and the information provided by each item. First, they agreed with the shortening of the questionnaire: true/false questions could be replaced by multiple-choice questions (one correct answer out of a four options). In that way, extra information about the same topic could be provided in the options. Thus, four items of the initial version of the questionnaire regarding aesthetic topics, misconceptions and correct knowledge were reduced to one, without losing information. For instance, four items such as ‘The function of the trunk musculature is control back stability and support the viscera’, ‘The trunk musculature supports fat from the abdomen and the waist’, ‘The trunk musculature is to embellish the body’ and ‘The trunk musculature is to get a flatter abdomen’, were finally reduced to one item: ‘The function of the trunk musculature is:’ (Electronic supplementary material Appendix, v7).
Second, the experts pointed out the need of making language more comprehensible for adolescents, avoiding the use of the double negative in writing.
After the changes were made from the experts’ suggestions, the questionnaire contained 24 items. This second version (Phase III) was evaluated by a set of participants by means of a group analysis session. Ten representative students of different age groups evaluated the comprehensibility, the ease of use of the questionnaire and they were asked about their beliefs on the body use in daily life physical activity. Two researchers presented the questionnaire to the students and the most important suggestions were registered. They were addressed to: topics about spine knowledge (such as form, function and body posture), language used and the comprehensibility of the questions. These suggestions were especially useful to improve the instructions for the administration session and to re-consider some of the alternative wrong answer options in the questionnaire. For instance, one of the wrong beliefs students had and which we included in the questionnaire was: “When standing for a while without moving, I should remain as steady as possible” (Electronic supplementary material Appendix, v10, option d).
The information provided by these ten users motivated the final version (Phase IV) of the HEBACAKNOW questionnaire (Electronic supplementary material Appendix). The resulting 24 multiple choice items were associated with one of the following categories according to conceptual knowledge: topographical-anatomical knowledge (items 1, 2, 3 and 6); functional–anatomical knowledge (items 4, 5 and 7); habits in standing posture (items 8–10); or seated (items 11–13); or lying (items 23 and 24); habits in carrying heavy objects in a backpack (items 14–18); and how to move heavy loads (items 19–22). The score for each item was 0 (wrong option) or 1 (correct option). The scores for each category and for the total questionnaire were obtained computing the mean value of the items involved. All the items had the same weight.
Procedure
The questionnaire administration took place in the IT classrooms using the web Moodle platform. Participation was optional. One of the researchers introduced the questionnaire to the students, explained the procedure to fill in, and solved the participants’ doubts. After a 4-week delay the second administration of the questionnaire was made. For this second session the items were presented in a different order to the same participants.
Participants
The study sample was made up of 230 students from four state secondary schools of Valencia (Spain). Only 171 students (82 male and 89 female), aged 14–17 (M 15.23, SD 1.33), completed the two rounds of the questionnaire. Students belonged to intact groups in several schools. These schools were selected by a simple random sampling method. The school headmasters, the tutor teachers from each group, and parents were informed and they gave written consent to students’ participation in the study. The project of this paper was sent to the ethics committee of the authors’ University and the approval was obtained.
Data analysis
The scores of each category and the total questionnaire were obtained. Calculating the mean value of the items were involved. Different statistical analyses were made for these scores using SPSS (v.19) software for Mac.
Cronbach’s alpha was used to test internal consistency.
Test–retest reliability was expressed according to several indicators: the differences observed between the readings (test1–test2) and the standard deviation of the differences, intraclass correlation coefficient [
25], 95 % confidence intervals for intraclass correlation coefficient, coefficient of repeatability and standard error of the mean and minimal detectable change [
26]. A 95 % confidence level for the minimal detectable change (corresponding to a
z value of 1.96) was established. Intraclass correlation coefficient of less than 0.40, 0.40 to 0.75, or greater than 0.75 was associated to poor, moderate, and excellent agreement respectively [
27].
Non-parametric tests were used when the variables were not normally distributed. The Wilcoxon signed-rank test was selected to analyse systematic differences between the two administrations of the test. The mean value and standard deviation of the test1–test2 differences were calculated and tested for significance using a one-sample t test (i.e. testing differences against zero). In addition, using the Bland–Altman graph, a plot of the differences between tests 1 and 2 against the mean value of the total score of the HEBACAKNOW questionnaire was used to obtain the agreement between the reported values at the individual level (95 % limits of agreement). The association between the difference and the magnitude of the total score of HEBACAKNOW questionnaire (i.e. heteroscedasticity) was examined by regression analysis.
Floor/ceiling effects were calculated from the percentage of adolescents showing the highest [
1] or lowest (0) value in total score at test 1. These effects were considered present when more than 15 % of the participants achieve the lowest/highest values [
28].