Goal Attainment Scaling is used in clinical settings as person-centred outcome measure that measures the extent to which an individual’s personal goals for treatment are achieved.
An important feature of GAS is the "a priori" establishment of criteria for a "successful" outcome in that individual, which is agreed with the patient and family before intervention starts so that everyone has a realistic expectation of what is likely to be achieved, and agrees that this would be worth striving for.
Goals are set to reflect the patient’s current ability and expected level of achievement within a specific length of time. Scoring of individual GAS goals is completed in a standardised way on a 5-point scale and converted to a T-score to provide a single figure that reflects the overall extent of achievement and allows for statistical analysis.
Prior to commencing treatment, clearly defined goals (usually 3-4) are identified by the patient, together with their treating team.
- The goals are refined through discussion to develop a ‘SMART’ goal statement that defined the expected outcome.
- SMART goal statement are specific, measurable, achievable, realistic, and timed to support accurate assessment of level of achievement.
The baseline level of function is recorded for each goal:
- Do they have some level of ability in relation to that goal (Baseline score -1)
- Or none at all – ie there is no plausible worse condition (Baseline score -2)
Optionally, goals can also be weighted to take account of the level of importance to the patient and/or the anticipated difficulty in achieving the goal.
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Level of importance
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Level of difficulty
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0 = Not important
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0 = Not difficult
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1 = Important
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1 = Minor difficulty
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2 = Very Important
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2 = Moderate difficulty
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3 = Extremely important
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3 = Extreme difficulty
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At the end of the treatment period:
Achievement of each GAS goal set, is rated on a 5-point scale (-2 to +2)
- If the goal is achieved as expected: - Score 0
- If better than expected: Score +1 (for ‘a little more’) or +2 (for ‘a lot more’)
- If less than expected: Score -1 (for ‘a little less’) or -2 (for ‘a lot less’)
In GAS as originally described:
Pre-defined descriptions for each of the 5 outcome scores are written prior to treatment and used as a “follow-up” guide to aid scoring at the end of treatment.
GAS T-scores are derived by applying the following formula:
GAS T-score = 50 +
Where:
wi = the weight assigned to the ith goal (if equal weights, wi = 1)
xi = the numerical value achieved ( between –2 and + 2)
p = the expected correlation of the goal scales
The GAS-light is a simplified version of GAS that is more conducive for completion in a busy rehabilitation setting.
- Rather than predefining each of the 5 levels in a “follow up” guide, just the SMART goal statement for the “0’ score is recorded
- Instead of the 5-point numerical score, a 6-point verbal rating is used which better reflects how clinicians think
- If the SMART goal was either over- or under- achieved, the reason for variance is recorded.
The verbal rating
The verbal scoring system is shown below:
To avoid having to apply a complicated formula, a GAS T-Score calculator is used to derive
- a baseline GAS T-score
- achieved GAS T-score (which provides an overall rating of achievement across all goal areas).
- change GAS T-score (difference between baseline and T-score).
Goal weighting can be recorded for the purposes of interpretation and team reflection on outcome, but is not used within the formula.
The GAS-eous is semi-structured version of GAS that was designed specifically for use in upper limb spasticity.
The GAS-eous uses the GAS-light approach to scoring but:
- Goals are structured into 2 predefined goal areas each with 4 goal areas
- Within each goal area, there are defined with subcategories and suggested goal parameters for defining the SMART goal
Find out more about the GAS-eous tool.
The common goal areas were developed through extensive goals analysis (see development tab) and are as follows:
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Domain 1
Impairment/Symptoms
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Domain 2
Activities/Function
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Goal Areas
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Pain/Discomfort
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Passive function
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Involuntary movements
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Active function
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Range of movement/prevention of contractures
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Mobility
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Cosmesis
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Facilitating therapy
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The GAS-legs is a semi-structured version of GAS that was designed specifically for use in lower limb spasticity.
It uses the same domains and goal areas as the GAS-eous, but with subcategories and suggested goal parameters adapted to suit the lower limb.
Find out more about the GAS-legs tool.