Detailled Information

Name of the Instrument/Tool Bath Ankylosing Spondylitis Disease Activity Score (BASDAI)
First Description

Garrett S, Jenkinson T, Kennedy LG, Whitelock H, Gaisford P, Calin A. A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index. J Rheumatol 1994;21(12):2286–91.

Year 1994
Concept of constructs Disease activity
Population/Disease Disease specific
Originally developed for Ankylosing spondylitis (AS)
Other rheumatic diseases
where can be applied (only if validated)
Axial Spondyloarthritis, Psoriatic Arthritis (PsA)
Additional population with no rheumatic diseases No
Language: Originally published in English
Available in Language Arabic, Chinese, Croatian, Czech, Danish, Dutch, English, Finnish, French, German, Hungarian, Norwegian, Portuguese, Romanian, Russian, Spanish, Swedish, Turkish, Ukrainian
Author/s Garrett S
Title A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index.
Journal J Rheumatol
Year 1994
Vol 21
Num 12
Pages 2286–91
Country United Kingdom
Language English
Other references of interest
Brief Description

Reproducibility of the Bath Ankylosing Spondylitis Indices of disease activity (BASDAI), functional status (BASFI) and overall well-being (BAS-G) in anti-tumour necrosis factor-treated spondyloarthropathy patients.

Brief Description

Establishment of the minimum clinically important difference for the bath ankylosing spondylitis indices.

Brief Description

Evaluation of the smallest detectable difference in outcome or process variables in ankylosing spondylitis.

Instrument/Tool Translations References
Brief Description

A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index (English).

Brief Description

Portuguese version of the Bath indices for ankylosing spondylitis patients: a cross-cultural adaptation and validation.

Brief Description

Evaluation of a French version of the Bath Ankylosing Spondylitis Disease Activity Index in patients with spondyloarthropathy.

Correspondence to Dr Andrei Calin
Address The Coach House, Linden Gardens, Bath, BA1 2YB, UK
Website ---
Available ---

The BASDAI questionnaire using VAS is available in the original publication. Available online (in multiple translations) at and at

Type Of Measure Questionnaire
Brief Description

Patient self-administered questionnaire used to measure patient-reported disease activity in patients with AS/axial SpA. The instrument was first published in 1994 using visual analogue scales. The use of numerical rating scales has also been validated. The index includes patient-reported levels of back pain, fatigue, peripheral joint pain and swelling, localized tenderness, and the duration and severity of morning stiffness.

Number of Items 6
Range 0-10
Responses options/scale Yes
0–10 cm) anchored by adjectival descriptors “none” and “very severe.” Duration of morning stiffness is anchored by a time scale (0–2 or more hours).
Developed for Both
Method of administration Self-administered
Recommendations to score

The scores for questions 5 and 6 (severity and duration of morning stiffness) are averaged; the result is then averaged with the remaining 4 question scores to give a final score out of 10.

Score Interpretation Ranges from 0 (no disease activity) to 10 (maximal disease activity).
Cut-off points Define: A cut off of ≥4 is used to define active disease. Reference percentile charts have been published. A 50% or 2 units (0-10) improvement in BASDAI with an intervention has been defined as a response to that intervention.
Cut-off points applied to Both
Smallest detectable change if described ---
Smallest detectable change applied to ---
Completion time by the patient between 30 seconds and 2 minutes (average 67 seconds). minutes
Scoring time by the assessor - minutes
Training to score Not necessary
Strengths Useful in clinical practice & research, Widely used
Limitations ---
Limitations >=5 European languages (English)
Observations ---
A. Internal Consistency Tested
Cronbach's (Describe)

α = 0.84-0.87

B. Reliability intraobserver or test-retest Tested
Continuous scores: intraclass
correlation coefficient (ICC)
Dichotomus: Cohen kappa (Describe)

ICC = 0.94 (0.91–0.95)

C. Reliability interobserver or Measurement error Tested
Standard error of measurement (SEM),
smallest detectable change (SDC) or
Limits of agreement (LoA) (Describe)

SDD = 1.96

95% CI of 95% limits of agreement = -2.32 to 2.23

A. Content validity: face validity Tested
Expert opinion (relevance and
comprehensiveness) (Describe)

Developed by experts in the field with patient input (however the role of patients is not made explicit).

B. Construct Validity:
Structural validity
Not Tested
Brief Description

Evidence using principal component analysis supports structural validity of the single domains of the BASDAI.


BASDAI correlated well with the earlier Bath Disease Activity Index with no significant differences in score distribution, reproducibility, or sensitivity.

Hypotheses-testing Tested
Brief Description

Good correlation with the Ankylosing Spondylitis Quality of Life questionnaire (Pearson’s correlation coefficient = 0.79) and BASDAI was significantly higher in AS patients unable to work due to AS.

Moderate correlation with BASFI (Spearman´s correlation coefficient = 0.45), SF36-PCS (Spearman´s correlation coefficient = -0.47) and weak correlation with SF36-MCS (Spearman´s correlation coefficient = -0.25).

Cross-cultural validity Tested
Brief Description

BASDAI has been translated, adapted and validated in several languages and countries.

C. Criterion validity Not Tested
Comparison with a 'gold standard' Continuous scores:
correlations, ROC curves Dichotomus:
Sensitivity & Specificity (Describe)
Responsiveness Tested
Ability to detect change over
time Multiple methods (Describe)

The modified standardized response mean measured against AS health transition is reported as -0.74 for improvement and 0.60 for deterioration in health (p<0.01), and measured against general health transition is -1.02 for improvement and 0.74 for deterioration.

Initial evaluation of the patient acceptable symptom state (PASS) in AS patients (Dougados et al) found the mean change in BASDAI over 12 weeks for the patient to feel well was -3.5 (SD 2.3), and there was significant correlation between the BASDAI 50% responders and patients achieving PASS. A PASS cut off of 3.45 cm (95% CI 3.09–3.89 cm) has been described.

Interpretability Tested
of responders with the highest/lowest
score Minimal important difference (MID) (Describe)

Distribution of scores across the scale has been shown to be good (score range: 0.5-10; mean: 4.31 in the first description). There have been no floor or ceiling effects reported.

MCID = 1 cm or 22.5% (with SE=65% and SP=82%, on ROC curve analysis using patient report of important change as the gold-standard).

Another study indicated that the smallest detectable difference was 1.96 (in a 0-10 scale), based on Bland-Altman´s technique.

Other Comments

A comparison of the Bath Ankylosing Spondylitis Disease Activity Index and a modified version of the index (mini-BASDAI) in assessing disease activity in patients with ankylosing spondylitis without peripheral manifestations was published in 2009 by Song et al (

Mini-BASDAI excludes the questions about peripheral arthritis (question 3) and enthesitis (question 4).

The authors assessed the correlation of the original BASDAI and the mini-BASDAI with patient global and other disease parameters was assessed in a total of 692 patients from three AS cohorts including one observational AS cohort and two clinical trial populations treated with non-steroidal anti-inflammatory drugs and tumour necrosis factor alpha inhibitors. Sensitivity to change was also assessed by calculating effect sizes.

The mini-BASDAI had higher values compared with the original BASDAI, also in the subgroup with peripheral manifestations. However, the mini-BASDAI did not correlate better with other markers of disease activity compared with the original BASDAI. Furthermore, effect sizes of the original BASDAI and mini-BASDAI were comparable in the treatment trials. Approximately 5% of active AS patients with pure axial disease manifestation were identified whose disease activity was underestimated by the original BASDAI.

The authors concluded that on a group level using the mini-BASDAI did not result in an advantage to assess disease activity or in the subgroup without peripheral involvement. In only approximately 5% of AS patients was the mini-BASDAI superior to the original BASDAI.

Outcome Measure ---