Introduction

Ankylosing spondylitis (AS) is a chronic inflammatory disease that can lead to a functional disability and deterioration of quality of life. The assessment of AS in different settings for disease control, symptom modification, and clinical record keeping is currently done through endpoints emphasizing disease activity and function. Currently, there are three instruments that are reliable, valid, and sensitive to change that have been recommended by the AS Assessment (ASAS) Working Group to measure such domains. Of these, the Bath Ankylosing Disease Activity Index (BASDAI) measures disease activity while the two others, the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Dougados Functional Index, measure functioning [1–3]. They have been selected by ASAS in the international consensus for the use and evaluation of efficacy of anti-tumor necrosis factor alpha [4]. For clinical use, self-report of health by patients needs cultural adaptation. Therefore, these instruments were translated into many languages and cultures. Thus, it was necessary to adapt these indices to the Moroccan linguistic and cultural context. The use of the same instrument has the advantage of allowing comparison between international trials in different countries. The aim of this study was to develop the Moroccan version of the BASFI and the BASDAI and to evaluate their validity and reliability.

Patients and methods

A prospective study was conducted from June 2007 to December 2008. The outpatients who fulfilled the modified New York criteria were included. They all were Moroccan; they spoke Moroccan Arabic, as their first language, dialectal Arabic. They gave their agreement to participate in the study. The study protocol was approved by the local ethics committee. Two visits, with at least 24-h to 1-week test–retest, were done for each patient. No modification of the treatment was authorized between the two visits.

The criteria of exclusion were an age lower than 18 years or the presence of severe comorbidity.

The social demographic data (age, sex, educational level,…) as well as clinical, biological, and radiological data relating to the AS (spinal pain and stiffness, number of nocturnal awakenings, number of painful and swollen joints, total enthesitis count, morning stiffness, erythrocyte sedimentation rate (ESR), radiological changes in the sacroiliac joints) were collected for each patient. During the first visit, we also evaluated the following parameters for each patient:

  • BAS-G [4] Bath Ankylosing Spondylitis Global Score

  • BASMI [5] Bath Ankylosing Spondylitis Metrology Index

  • BASRI [6] Bath Ankylosing Spondylitis Radiology Index

Original questionnaires

The BASFI is a quick, simple, relevant, and sensitive to change questionnaire. It is comprised of ten items [2]. Each item is graduated from 0 to 10 (0 = easy, 10 = impossible). The first eight items reflect activity relating to the functional ability of patients, and the two additional questions assess the patient’s ability to cope with everyday life.

The BASDAI is a six-item self-administered questionnaire that measures symptoms such as fatigue, spinal pain, pain, and/or swelling of the peripheral joints, localized tenderness, and morning stiffness during the last week [3]. Questions are presented in the form: “how would you describe the overall level of….” It also measures the severity and duration of stiffness (0 to 2 h or more). The first five items are answered on 0–100-mm visual analog scales (VAS) with “none” anchored at one extreme and “very severe” at the other.

Translation–adaptation

The Moroccan version of these instruments was obtained, in accordance with the guidelines for this process, in order to preserve equivalence between the original and the target version [2, 7–10]. The translation of BASFI and BASDAI was made in several steps: First, BASDAI and BASFI were translated into Moroccan language separately by two bilingual Moroccan teachers of English (translation T1 and translation T2). They were made aware of the objectives underling the material to be translated to obtain a better idiomatic and conceptual translation rather than simple literal equivalence. They produced a T1–2 version which was back translated by two groups of bilingual back translators (back translation BT1 and BT2). They produced a BT1–2 version. All the translations were compared during a meeting. The multidisciplinary committee of experts was made up of a sociologist, an expert in linguistics, the translators, the back translators, a monolingual, and two rheumatologists. It produced the pre-final version, which was submitted into the pretest.

Acceptability

The acceptability of the questionnaire was tested by analyzing the percentage of refusals, the missing data, percentage of discordances, and the items which were difficult to understand.

Psychometric properties and statistical analysis

Construct validity

Structural validity was tested by the study of the correlation matrix which represented the correlation between different items. It was a strong correlation if r was higher than 0.60; moderate correlation if r was between 0.30 and 0.60; small correlation if r was lower than 0.30 [11, 12]. The correlation was obtained with Spearman’s coefficient.

For assessing external construct validity, the BASFI was compared with clinical, biological, and radiological variables that can evaluate functional status [2, 7, 8]. The correlation between these parameters was given as Spearman’s correlation coefficient (r); the values of this coefficient were interpreted in the following way: Excellent correlation if r was equal to or higher than 0.91, good correlation if r was between 0.90 and 0.71, moderate correlation if r was between 0.70 and 0.51, poor correlation if r was between 0.50 and 0.31, and small or absent correlation if r was lower or equal to 0.30 [11–13].

Reliability

Reliability was analyzed by internal consistency and reproducibility. The internal consistency was appreciated by Cronbach’s coefficient alpha. The more it is approximate to 1, the better it is. A high value of this coefficient (≥0.70) was usually regarded as satisfactory [13, 14]. Reproducibility test–retest was appreciated by intraclass correlation coefficient (ICC). The ICC is a quantitative test. A value higher than 0.80 is usually regarded as satisfactory [13].

Statistical analysis was carried out using the SPSS for windows version 13 (SPSS, Chicago, IL, USA).

Results

Patients’ characteristics

Eighty-five Moroccan patients suffering from AS were recruited. Sixty-two men (73%) and twenty-three women were included, with a mean age of 35.5 years. The duration of their illness was variable, ranging between 2 and 26 years. A severe form of AS was noted (hip disease in 54% with functional disability (BASFI > 4) in 58.8%. An active form was noted in 63.5% cases [BASDAI > 4] (Table 1).

Table 1 Demographic and clinical data for 85 patients with AS
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Final version of the Moroccan BASFI and BASDAI

Globally, the cross-cultural adaptation of the BASFI did not present any difficulties during the translation process. However, some modifications were necessary to adapt to the Moroccan cultural context:

The examples “sock aid” and “helping hand” from items 1 and 3 were deleted from the Moroccan version because these instruments were neither known nor used by the majority of the Moroccan patients. Figure 1 represents the final version of the BASFI.

Fig. 1
figure 1

Moroccan Arabic version of BASFI

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The cross-cultural adaptation of the BASDAI did not lead to any difficulties during the translation process. No items were modified or simplified. The Moroccan Arabic version of the BASDAI is represented in Fig. 2.

Fig. 2
figure 2

Moroccan Arabic version of BASDAI

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Acceptability

Acceptability, evaluated by the rate of response, was 100%. All items were comprehensible, and no missing data were noted.

Psychometric properties

Structural validity

There was moderate correlation between different items of the BASFI and the BASDAI (Table 2).

Table 2 External construct validity of the BASFI and the BASDAI
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External construct validity

There is statistically significant correlation between the BASFI and the BASDAI, the BAS-G, the BASMI, the BASRI, the Schober’s test, the chest expansion, the finger ground distance, the occipital wall distance, the spinal pain, the radiological changes in sacroiliac joints, and ESR. No correlation was observed between BASFI and enthesitis index (Table 2). BASDAI was correlated with the number of nocturnal awakenings, the morning stiffness, the VAS of the activity, the spinal pain, the painful joints index, the enthesitis index, the BAS-G, the BASFI, erythrocyte sedimentation rate, and the BASMI. No correlation was noted between the BASDAI, the BASRI, and the number of swollen joints (Table 2).

Reliability

Internal consistency measured by the Chronbach’s alpha was 0.90 for the BASFI and 0.86 for the BASDAI.

Test–retest reliability measured by the ICC was 0.96 (confidence interval (CI) at 95% = 0.93–0.97) for the BASFI (Table 3) and 0.93 (CI at 95% = 0.90–0.95) for the BASDAI (Table 4).

Table 3 Reliability of the BASFI measured with the intraclass correlation coefficient
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Table 4 Reliability of the BASDAI measured with the intraclass correlation coefficient
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Discussion

Physical function and disease activity are important outcome measures in AS clinical trials. The ASAS working group has recommended the use of the BASFI for the domain of physical function in core sets for medical treatment. The BASDAI evaluates the domain of disease activity in ASAS recommendations. The aim of the standardization of these tools is that the results of an evaluation of disease progression and treatment effects become comparable among different studies in different countries and cultures. This study is a trial for the standardization of the BASFI and the BASDAI to suit the Moroccan and Arabic culture. The cross-culturally adapted versions of the BASDAI and the BASFI produced in this study maintained all the properties of the original English language versions of the instruments. The BASFI was translated into several languages. After the French version [13], several countries translated and validated this instrument: Sweden [14], Germany [15], Finland [16], Spain [17], and recently Turkey [18] and the Romania [19]. The BASDAI was translated into French [20], Swedish [21], German [22], Spanish [23], and Turkish [24] languages. The BASFI and BASDAI were recently translated into classical Arabic but are not adapted to our local idioms and cultural context [12].

The Moroccan version of the BASDAI did not require any major cultural adaptation in the translation process, and in many other countries, a simple literal translation was necessary [14–18].

The statistical analyses of the Moroccan version of the BASFI showed a strong reliability. Our result was comparable with the French [15], Finnish [18], Swedish [21], German [22], Turkish [24], and Rumanian [19] versions. ICC ranged between 0.82 [21] and 0.99 [18]. The reliability of this instrument in the Spanish version was acceptable (ICC = 0.68). Cronbach’s alpha was satisfactory in our study (alpha = 0.90); this data was comparable with the data of the literature where alpha ranged between 0.81 [17] and 0.94 [18]. The structural validity was appreciated only in the Swedish, French, Turkish, and Moroccan versions with a statistically significant correlation between items (p < 0.001), showing the homogeneity of items and one-dimensional context of the measured phenomenon by the BASFI which is the functional status. The most important parameters measured to assess external construct validity in all versions were Schober’s test, finger ground distance, occipital wall distance, and chest expansion. A statistically significant correlation was found for all these parameters. The reliability of the BASDAI was excellent in our version; it joined the data of the original, Swedish, and Turkish versions. Structural validity was studied in the Turkish, Swedish, French, and our version. A statistically significant correlation between items was noted with strong correlation between items 2 (the spinal pain), 3 (peripheral pain), 5, and 6 (intensity and duration of the morning stiffness). Indeed, these items constitute the main clinical indicators of the evaluation of the activity in AS. The parameters used for the assessment of the external construct validity were different from one study to another [21–24]. However, we noted a preferential use of the following variables: the number of nocturnal awakenings, the morning stiffness, analogical visual scale of pain, the erythrocyte sedimentation rate with a statistically significant correlation between the BASDAI, and the various parameters in the other studies [25].

Conclusion

The Moroccan version of BASFI and BASDAI are both reliable and valid; they can be self-administered to Arabic AS patients to evaluate their functional disability and disease activity.