Ethics approval for this study was obtained by the Canton of Zürich ethics review board (KEK-ZH-Nr.2010-0252/5).
Translation
The translation and cross cultural adaptation were based on the guidelines of Beaton, Bombardier et al. [4]. The entire process is made up of 6 steps (Figure 1).
Stage 1
Two translators (T1 and T2) translated independently the questionnaire from English into German. Both T1 and T2 had German as their mother language but were also fluent in English. One of the translators (T1) is a chiropractor in Switzerland (clinician) and the second (T2) is a Swiss librarian (linguist). They both provided a written report.
Stage 2
The two independent translated versions TV1 and TV2 were revised by consensus agreement to TV1-2 by the original translators, and overseen by the expert committee.
Stage 3
The agreed TV1-2 version was then back translated by two independent translators (BT1 and BT2). Both back translators had English as their first language but were fluent in German. BT1 and BT2 were both chiropractors from Canada working in the German speaking part of Switzerland for several years. They were blinded to the original version of the Bournemouth questionnaire. Their two versions of the back translation (BTV1 and BTV2) were submitted to the committee.
Stage 4
An expert committee reviewed all reports and agreed by consensus to a pre-final version of the German Bournemouth questionnaire. This team of 8 people was made up of methodologists, health professionals, language professionals, and translators. The original developer of the English version of the BQN also participated in an advisory capacity.
Stage 5
The pre-final form of the BQN was tested on a sample of 30 patients in a chiropractic practice in Zürich, Switzerland for face validity. The neck pain patients were asked to complete the questionnaire after having treatment. Afterwards the questionnaire was discussed with the patient item by item and they were asked to explain their understanding of the meaning of each question. The patients were also asked if they had any problems with the format, instructions, response scales or layout of the questionnaire.
Stage 6
A written report on the face validity of the questionnaire was sent to the expert committee. Each member of the committee also made a written report. Minor changes were agreed and the pre-final form was modified to include these changes with consensus. This version then became the final German version of the BQN for validation testing (Additional file 1).
Test-Retest Reliability
Data for the test-retest reliability study was collected during a lecture for medical students in order to ensure that the participants did not sustain any neck trauma or undergo any treatment between completing the two questionnaires. Students with neck pain were asked to complete the German version of the BQN prior to the start of the lecture. After two hours they were asked once again to fill in the BQN, but they were not told that it would be the exact same questionnaire. To protect anonymity, the students had to write the first two letters of their mother's name and the birth year of their mother on the top of the page so that the pre-lecture and post-lecture questionnaires could be matched. In order to obtain 31 participants, this same process was repeated before and after a two hour meeting of chiropractors.
Validation
Cross-cultural adaptation tries to ensure consistency in the content and face validity between the original and the translated versions of a questionnaire, but it does not ensure that the questionnaire has construct validity. Content validity was already specifically evaluated on the original English version of the questionnaire, and was therefore not tested in this German version. Additional testing was done to evaluate construct validity however [13, 14]. This additional testing of the instrument was done in the same population where it would be used, as recommended in the literature [10]. The BQ is commonly used as an outcome measure for neck and low back pain patients being treated by chiropractors in the UK, where it was developed, as well as in other countries (9,11,13). Thus 128 neck pain patients from two different chiropractic practices were asked to fill in the new German version of the BQN, the German version of the NDI [5] and the German version of the NPAD [15] prior to the start of their chiropractic treatment-series. After finishing the treatment series or 4 weeks later, each patient had to complete the 3 questionnaires again. The questionnaires were given to them in the practice or sent by post with an addressed and stamped return envelope. Those patients who received them in the practice filled them in immediately. Those who received them by post were allowed one week to return them. If the questionnaires were not returned within 1 week, the patients were called by phone and reminded to return the completed questionnaires. If necessary, the questionnaires were resent to the patients. The NDI and NPAD were chosen as they contain similar subscales to the BQN. To compare questionnaires, each instrument was broken down into its component subscales. Figure 2 shows the matching of the various subscales on the NPAD and NDI questionnaires with the seven subscales on the Bournemouth questionnaire.
Statistical Analysis
Test-retest reliability of the BQN was evaluated using the two way mixed Intraclass Correlation Coefficient (ICC) [10, 13, 16]. The internal consistency of the BQN, which measures the degree to which items that make up the total score are all measuring the same underlying attribute, was assessed using Cronbach α [10, 13, 16].
External construct validity shows the extent to which the BQN's scores concord with the scores of other instruments measuring the same theoretical hypotheses of the concepts under consideration [13]. This was done using the Pearson's correlation coefficient comparing the 7 scales and total score of the BQN with the NDI as well as the BQN with the NPAD for answers given at baseline (pre-treatment) and at 4 weeks after the start of treatment [14]. External longitudinal construct validity was determined with Pearson's correlation of the change scores of the various scales comparing the BQN with the other two questionnaires over the 4 week treatment period.
The sensitivity to change over time of the three questionnaires was assessed with the standardized response mean (SRM). The average change in scores for each scale was divided by the standard deviation of the score changes [13, 17].