Patients and design
This study was approved by the Ethics Committee of Costa del Sol, March 2014, Spain. All participants in the study gave a written informed consent. Participants were recruited from six primary health care centres in the province of Malaga, Spain. Participants met the following inclusion criteria: i) shoulder pain, defined as “pain in the shoulder region brought on or exacerbated by movement at that shoulder”. ii) aged between 18 and 80 years, iii) first language was Spanish (Spain), iv) able to read written Spanish. Participants were excluded from the study if they did not have the capacity to comprehend the questionnaire due to cognitive or emotional impairment. Prior to conducting study, the authors obtained permission for the original author (Dr KE Roach), who was also involved in the study.
The study consisted of two phases
The study was conducted in two phases. The first was thehe cross-cultural adaptation of the SPADI and the second was the validation of the adapted SPADI. The cross-cultural adaptation process was undertaken using the guidelines and methodology recommended by the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) for the translation and validation of patients reported outcome measures [19]. The validation of the adapted SPADI was then undertaken by examining its psychometric properties and conducting a confirmatory factor analysis.
Cross-cultural adaptation
Cross-cultural adaptation involved eight stages: (1) forward translation, (2) reconciliation; (3) back translation, (4) back translation review, (5) harmonisation, (6) pilot testing/cognitive debriefing, (7) pilot testing review/review of cognitive debriefing results and (8) proofreading.
Forward translation
Two forward translations in Spanish were undertaken from the original English language version of the SPADI. The translations were undertaken by two independent health professionals who were native residents of Spain and fluent in both Spanish and English.
Forward translation reconciliation
The two forward translations were reconciled into one version (draft 1) by the two original translators, a third independent translator, and with additional input from the project lead.
Back translation
Two professional English native translators residing in Spain back translated the reconciled Spanish language version (draft 1) into English independently. The translators had neither prior knowledge of the SPADI nor of the original wording of the English version of the SPADI.
Back translation review
The principal investigator and a native Spanish speaker fluent in both languages reviewed the back translation for any discrepancies in meaning or terminology used. Any problematic item was discussed until the discrepancies were resolved. This process resulted in a refined second draft of the Spanish translation (draft 2).
Harmonisation
To produce the final Spanish language translation, a harmonisation meeting was undertaken involving three Spanish translators, the senior investigator and the developer of the original USA version of the SPADI. During this meeting, any discrepancies or issues that were highlighted from the back translation were discussed, the translated version of the SPADI was evaluated and a final version agreed.
Pilot testing/cognitive debriefing
Once the translation process was completed, the translation was formatted to match precisely the original American language version. The translated SPADI version was initially assessed for comprehensibility in five patient participants, who were Spanish residents and native speakers, met the inclusion criteria described above and had a low educational background without being illiterate. At this stage, each participant was asked by the in-country investigator to carry out the following tasks:
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To complete a copy of the translated SPADI and time needed.
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To comment on the response options within the back-translated SPADI.
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To comment on any wording that was difficult to understand.
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To suggest alternative wording/phrasing for any wording that was difficult to understand.
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To describe in their own words what the wording meant to them. These responses were recorded verbatim and translated into English. The five patients’ responses were summarised by the senior investigator. This summary also contained any changes, recommendations or suggestions indicated by the participants and in-country investigators.
Pilot testing review/review of cognitive debriefing results
To improve the performance of the translated questionnaire, the pilot testing results were reviewed by the in-country investigators. At this stage, any item that caused comprehensibility difficulties for more of the 40 % of the participants was reviewed, and any modifications suggested by the respondent’s comments were incorporate to the final translated version.
Proof-reading
The senior investigator and a translator, who was not involved in the translation process previously, independently proofread the final formatted translation, and any suggested changes were discussed with the senior investigator. Furthermore, the Flesh Reading Ease test and the Flesh Kincaid Grade Level were calculated for readability [20].
Following this process, a final draft of the SPADI translated and culturally adapted into ‘Spanish for Spain’ was locked down and entered into the cross-cultural validation phase (final draft).
Validation phase
Before completing the questionnaire, the following data were recorded: age, sex, professional status, education level, affected shoulder and diagnosis. The questionnaires were administered by physical therapists working in the six different physical therapy rooms. They addressed any possible concern of the subjects. Items were numbered from 1 to 13. Items 1 to 5 were from pain subscale and items 6 to 13 were from disability subscale.
Sample size calculation
To test a two-factor model, assuming the null hypothesis of a mean square error of approximation (RMSEA) from 0.04 to 0.085, with an alpha value of 0.05, a statistical power of 0.8 and a maximum of 26 degrees of freedom, as suggested by MacCallum et al [21], sample of 196 subjects was required which was over-estimated by 10 % to cover possible losses. The calculations were performed with the Statistica 12 software [22].
Data analysis
Descriptive statistics were carried out with means, standard deviations, and absolute and relative frequencies. Analysis of normality of distributions was evaluated by the Kolmogorov-Smirnov test, symmetry analysis and kurtosis. Internal consistency was calculated using Cronbach’s alpha. A Cronbach’s alpha between 0.70 and 0.95 was considered “good” [23]. Moreover, item-total and inter-item correlations were assessed. Pearson and Spearman correlations were calculated to assess the convergent validity between SPADI and quick-DASH-Spanish version [24]. To assess factor structure, a confirmatory factor analysis was done, the evaluated model was fit with the following parameters: the penalizing function (chi square/ df), which is indicative of good fit with values less than 3; Root Mean Square Error of Approximation (RMSEA) and confidence intervals (CI 90 %), taking the value 0.05 as cut-off of good fit; Normed Fit Index (NFI), the Comparative Fit Index (CFI), and Goodness of Fit Index (GFI) with a minimum value of good fit of 0.90. Multinormality was evaluated with the Mardia’s coefficient (multivariate curtosis), which could not be over “p” (p + 2), where “p” are the number of observed variables [25]. All the analyses were performed with SPSS 21 [26] and AMOS 21 [27].