[Definitive Edition] A Comprehensive Guide to the Reliability of the Berg Balance Scale (BBS)

[Positioning of this magazine] This article is positioned as Step 2: Major Balance Assessment Scales. The BBS evaluates balance ability from multiple perspectives using 14 items totaling 56 points. Combining it with the TUG allows for more accurate fall risk assessment.
Magazine: Evidence-Based Functional Assessment and Clinical Judgment https://note.com/shiraishi_pt/m/m277c678ca868

Do you have these concerns in clinical practice?

• When the BBS score changes, is it really an improvement?

• I understand that the ICC is high, but I don't really understand the MDC values.

• Does the reliability of the BBS change depending on the disease?

Terminology Explanation

I will explain in detail later, but briefly put...

In this article, based on the systematic review by Downs et al. (2013), we will
organize the relative reliability (ICC) and absolute reliability (MDC) of the BBS
by disease and score range.

What you will learn from this article

✔ The difference between relative reliability and absolute reliability and their clinical significance
✔ Pooled estimates of overall BBS ICC (intra-rater and inter-rater)
✔ How MDC95 changes depending on the score range
✔ The impact of ceiling and floor effects and points to note
✔ Reliability in cases with cognitive impairment

Conclusion (Key points first)

① Intra-rater ICC = 0.98 (95% CI 0.97–0.99) (Measured and compared by the same rater)
② Inter-rater ICC = 0.97 (95% CI 0.96–0.98) (Measured and compared by different raters)
③ MDC95 is 2.8–6.6 points
in the score range of 20–56④ MDC data for the 0–20 score range hardly exists
⑤ If cognitive impairment is severe, MDC may be as high as 7.7 points potentially

Basic Knowledge: The Difference Between Relative Reliability and Absolute Reliability

Relative Reliability (ICC)

• The value is expressed from 0 to 1, and the closer it is to 1, the higher the reliability.

• The greater the diversity (variation) within the group, the higher the ICC tends to be.

• Therefore, it cannot necessarily be said that "high ICC = clinically useful."

Absolute Reliability (MDC: Minimal Detectable Change)

• MDC95 is the threshold that can be judged as a true change with 95% confidence.

• More clinically useful than ICC for evaluating individual changes.

• Changes in group averages can be detected even if they are smaller than the MDC.

Summary of BBS Relative Reliability (ICC)

These are the results of a meta-analysis of 11 studies involving 668 participants.

Intra-rater ICC

The pooled estimate is 0.98 (95% CI 0.97–0.99) based on a meta-analysis of 3 studies (n=101). Heterogeneity between studies was low (I²=0%), indicating stable results.

The target conditions range from acute and chronic stroke to multiple sclerosis, and high intra-rater reliability has been confirmed for all.

Inter-rater ICC

The pooled estimate is 0.97 (95% CI 0.96–0.98) based on a meta-analysis of 5 studies (n=345). However, there is moderate heterogeneity between studies (I²=69%), so
caution is required regarding the variation in results.

Target conditions include stroke, multiple sclerosis, spinal cord injury, and the elderly, among
others.

Summary of BBS Absolute Reliability (MDC95)

The most important point is that MDC95 varies depending on the score range.

MDC95 for score range 20–56

All included studies targeted populations with an average BBS score of 20 or higher. The MDC95 (minimal detectable change with 95% confidence) for each score range is
as follows.

There is a tendency for the MDC to become smaller as the score increases. This is because the ceiling effect makes it easier for evaluators to agree on scores in the high-score range.

Overall, in the score range of 20–56, the authors' interpretation is that
'a change of 3–7 points can be considered a true change with 95% confidence.'

MDC for the 0–20 score range is unknown

Importantly, there is almost no MDC data available for the population with BBS scores of 0–20 (severe balance impairment)
.

For patients in this score range (unable to stand independently or requiring assisted walking), clinical judgments based on MDC should be made with caution.

When cognitive impairment is present

A
study (Conradsson et al., 2007) targeting nursing home residents with severe cognitive decline found that in a group with a mean BBS score of 30.1, the
MDC95 was 7.7 points, which was clearly higher than in other studies.

This indicates that cognitive decline affects measurement reproducibility, and
when applying the BBS to patients with cognitive impairment, a larger change may need to be used as the criterion for a 'true change'
.

Regarding ceiling and floor effects

Ceiling effect: In patients with BBS scores near 56 (maximum score), a score of 4/4 is given for almost all items, making it difficult to detect improvement. Studies on Parkinson's disease are affected by this, which may lead to an overestimation of reliability.

Floor effect: In patients with BBS scores near 0–15 (unable to stand independently), a score of 0/4 is given for almost all items, making it similarly difficult to detect change.

→ It is important to note that for patients with extreme scores (especially in the low score range), it is difficult to make clinical judgments based solely on BBS changes.

Clinical application

① When assessing individual change

If the BBS score changes by 3–7 points and the score is in the 20–56 range,
it may be a 'true change beyond measurement error.'
Make it a habit to check whether the amount of change reaches the MDC.

② When assessing group change (research or entire wards)

Changes in group averages can be statistically detected even if they are smaller than the MDC.
The criteria for individual judgment and group judgment differ.

③ Patients with severe balance or cognitive impairment

For patients with scores below 20 or severe cognitive impairment,
BBS MDC data is scarce, and there are limits to interpreting changes.
Consider using supplementary assessment tools (such as the TUG).

Common misconceptions

Misconception ①: 'If the ICC is 0.97, it is reliable for everything'

→ The ICC depends on the variability of the population.
It may be lower in homogeneous groups, and
'high ICC' does not necessarily mean 'clinically sufficient.'

Misconception ②: 'If the BBS increases by 2 points, the patient has improved'

→ It depends on the score range, but in many cases, the MDC95 is 3 to 7 points.
A change of 2 points may be within the range of measurement error.

Misconception 3: "The same MDC can be used for any disease"

→ The MDC varies depending on the score range, disease, and evaluation interval.
It is important to refer to the MDC values from studies that are close to the subject's score range.

Summary

• BBS intra-rater ICC = 0.98, inter-rater ICC = 0.97, indicating high relative reliability

• The MDC95 ranges from 2.8 to 6.6 points for scores between 20 and 56 (the higher the score, the smaller the value)

• There is almost no MDC data for scores 0–20, so caution is required when applying it to patients with severe balance impairment

• If cognitive impairment is severe, the MDC may be as high as 7.7 points

• Due to ceiling and floor effects, there are limits to detecting changes in patients with extreme scores

• For assessing individual changes, MDC (absolute reliability) is more useful than ICC (relative reliability)

References

Downs S, Marquez J, Chiarelli P.
The Berg Balance Scale has high intra- and inter-rater reliability but absolute reliability varies across the scale: a systematic review.
J Physiother. 2013; 59(2): 93–99.
doi: 10.1016/S1836-9553(13)70161-7

This article is based on the content of the paper above. Please use your clinical judgment when applying this to practice, taking into account the patient's condition, facility environment, and the latest evidence.

If you were able to use the BBS values with supporting evidence, I would appreciate it if you could press the Like button. Combining it with the TUG is effective for a comprehensive assessment of fall risk, and I have organized that process in my article on clinical decision flowcharts.

Related articles in this magazine

→ Fall Risk Assessment with TUG: A Complete Summary of Values and Interventions

→ Cut-off Values by Disease: Organizing Scale Criteria for Post-THA, TKA, and Proximal Femoral Fractures

→ Clinical Decision Flowchart: Visualizing Decisions on Fall Risk and Discharge Eligibility