Sunnybrook Neglect Assessment Procedure (SNAP)

Evidence Reviewed as of before: 12-04-2018
Author(s): Andréanne Labranche
Editor(s): Annabel McDermott OT
Expert Reviewer: Farrell Leibovitch
Content consistency: Gabriel Plumier

Purpose

The Sunnybrook Neglect Assessment Procedure (SNAP) is a test battery to screen for neglect in patients with acute stroke (Black et al., 2016).

In-Depth Review

Purpose of the measure

The Sunnybrook Neglect Assessment Procedure (SNAP) is a test battery for bedside screening of neglect. It is designed to assess neglect in patients with acute stroke and to monitor recovery of neglect at later stages of stroke recovery.

Available versions

There is one version of the SNAP.

Features of the measure

Items:

The SNAP is comprised of five paper-and-pencil items that are familiar measures of neglect. The items are administered to the patient in the following order:

  1. Spontaneous drawing of clock and daisy
  2. Line cancellation task
  3. Line bisection task
  4. Copying of clock and daisy
  5. Shape cancellation

Description of tasks:

A1. Drawing task
The patient is asked to draw a clock face and a daisy on a blank piece of paper.

B. Line Cancellation Task
The patient is instructed to cross out all lines on a page.

C. Line Bisection Task
The patient is instructed to draw a mark on a line in order to bisect the line in half. This task is completed using 15cm and 20cm lines.

A2. Copying Tasks
The patient is asked to copy a picture of a clock and a daisy.
Note: The assessor does not identify that the pictures are a clock and a daisy.

D. Shape Cancellation Task
The patient is required to circle all the targets on a page.
Note: This is a timed task. The patient is given a different color pencil after every tenth target is circled, to determine the search pattern.

Scoring and score interpretation:

The scoring of the different SNAP subtests is based on omissions made on the contralateral side of the brain lesion. Left-side omissions are scored in patients in right hemisphere stroke and right-side omissions are scored in left hemisphere stroke.

A. Copying and drawing tasks
Drawings with a significant omission of details on the contralateral side are scored as having neglect.

B. Line Cancellation
Each omitted line on the contralateral side of the page is scored as neglect.

C. Line Bisection 
The score for this task is based on the mean percent deviation of the patient’s mark from the true midpoint. Percent deviation and average deviation is calculated for the four lines of the task, according to the formula stipulated in the SNAP manual.

D.Shape cancellation task
All targets omitted on the contralateral side of the page are counted.

Total score interpretation:

Scores are calculated using the SNAP scoring manual. The patient is awarded a score for each subtest, resulting in a total score out of 100.

Leibovitch et al. (2012) recommended classifying severity of neglect according to performance on the SNAP as follows:

SNAP Score

Classification of Performance

0-5

Normal Performance

6-40

Mild Neglect

41-100

Severe Neglect

Please see the SNAP Administration and Scoring Manual for more details on scoring (Black et al., 2016).

What to consider before beginning:

SNAP test items should always be placed in the individual’s midline.

Time:

Time taken to administer the assessment has not been specified. Time will vary according to the patient’s attention and severity of neglect.

Training:

Training requirements have not been specified.

Subscales:

None.

Equipment:

  • SNAP assessment package
  • Two blank sheets of paper
  • Coloured pens/pencils
  • Stopwatch

Alternative forms of the SNAP

The original version of the Sunnybrook Neglect Assessment contained additional drawing tasks, a paragraph reading task, a writing task and additional visual search tasks. The four items that comprise the SNAP were deemed to be complementary and not redundant, so the additional items were eliminated (Leibovitch et al., 2012).

Client suitability

Can be used with:

Patients with stroke.

Should not be used with:

Not specified.

In what languages is the measure available?

English.

Summary

What does the tool measure? Hemispatial neglect
What types of clients can the tool be used for? Patients in the acute phase of stroke recovery.
What ICF domain is measured? Impairment.
Is this a screening or assessment tool? Screening.
Time to administer Not specified.
Versions There is one version of the SNAP.
Languages English.
Measurement Properties
Reliability

Internal Consistency:

One study reported moderate to excellent correlations between subtests and the total score.

Test-retest reliability:

No studies have reported on test-retest reliability among patients with stroke.

Intra-rater / inter-rater reliability:

One study reported adequate to excellent correlations for subtests and the total score.

Validity

Construct validity:

One study reported a moderate correlation among SNAP subtests.
Two studies have conducted factor analysis and found that all subtests loaded on one factor that accounted for 69-72% of the variance.

Convergent/discriminant validity:

One study reported adequate correlations with the visual search board (VSB) visual search task.
One study reported a significant correlation between neglect measured by the SNAP and parietal damage.
One study reported an excellent correlation between the SNAP and a measure of generalized attentional capacity (digit span forward minus digit span backward).

Known groups validity:

One study reported significant differences in performance on the SNAP according to side of lesion.

Criterion validity:

Concurrent validity:
No studies have reported on concurrent validity of the SNAP among patients with stroke.

Predictive validity:

One study reported that the SNAP significantly predicted neglect (present/absent) on the visual search board (VSB) visual search task.

Floor/Ceiling Effects No studies have reported on floor/ceiling effects among patients with stroke.
Sensitivity/ Specificity One study reported 68% sensitivity and 76% specificity.
Two studies reported that the shape cancellation task was the most sensitive subtest; a third study reported that the line bisection task was the most sensitive subtest.
One study reported that the drawing/copying subtests showed highest specificity.
Does the tool detect change in patients? The tool does not detect or measure change but it can be used to monitor change in neglect over time.
Acceptability The SNAP is simple to administer and can be used at the individual’s bedside.
Feasibility The SNAP is portable, quick to administer and requires minimal equipment.
How to obtain the tool?

The SNAP administration and scoring manual and test booklet can be accessed here

Psychometric Properties

Overview

A literature search was conducted to identify all relevant publications on the psychometric properties of the Sunnybrook Neglect Assessment Procedure (SNAP) for use with patients with stroke. Five articles were reviewed.

Floor/Ceiling Effects

Leibovitch et al (2012) examined psychometric properties of the SNAP in a sample of 224 patients with acute stroke and 100 elderly individuals. Results from the population of elderly individuals without stroke showed no omissions of details on the drawing/copying subtests and no omissions on the line cancellation subtest.

Reliability

Internal Consistency:

Leibovitch et al (2012) examined internal consistency of the SNAP in a sample of 224 stroke patients with acute stroke, using Cronbach’s coefficient alpha. All subtests showed an excellent correlation with the total neglect score (alpha = 0.84, p < 0.001) and correlations between subtests were moderate (alpha < 0.07, p < 0.0005). This indicates that subtests are measuring the same construct but are not redundant.

Test-retest reliability:

There are no studies of test-retest reliability of the SNAP among patients with stroke.

Intra-rater / inter-rater reliability:

Leibovitch et al (2012) examined intra-rater and inter-rater reliability in a sample of 12 patients with acute stroke and 12 elderly individuals. Intra-rater reliability was measured with 1 rater and inter-rater reliability was measured between 2 raters. Reliability was measured using Kappa statistics for drawing/copying tasks and interclass correlation coefficients for other scores. The authors reported adequate to excellent correlations for subtests and the total score (r = 0.73-0.99, p < 0.001); specific statistics were not provided.

Validity

Content validity:
Development of the SNAP is not reported.

Construct validity:
Black et al. (1995) examined construct validity of the SNAP in a sample of 294 patients with acute stroke. SNAP subtest scores correlated significantly (r = 0.4-0.6, p = 0,0001). Initial factor analysis showed that all four tests contributed to a single factor which accounted for 72% of the information contained in the four subtests.

Leibovitch et al. (2012) examined construct validity of the SNAP in a sample of 224 stroke patients with acute stroke, using factor analysis of subtest scores. Results revealed all subtests loaded equally on one factor that accounted for 69.4% of the total variance (eigenvalue = 2.8). Further factor analysis according to side of brain injury similarly showed that, among patients with right hemisphere damage, all four subtests loaded equally on one factor that accounted for 69% of the total variance. Results of patients with left hemisphere damage revealed two factors accounting for 62% of the total variance: the first factor comprised three subtests (drawing/copying, line cancellation and shape cancellation) and accounted for 37% of total variance; the second factor (line bisection) accounted for 25% of the total variance.

Convergent/discriminant validity:
Leibovitch et al. (2012) examined convergent validity of the SNAP by comparison with the visual search board (VSB) visual search task (Kimura, 1986) in a sample of 224 patients with acute stroke, using Receiver Operating Characteristic analysis. Results showed adequate validity (area under curve = 0.78).

Leibovitch et al. (1998) examined convergent validity of the SNAP by comparison with location and severity of brain damage on CT and SPECT scans in a sample of 120 patients with acute/subacute stroke, using regression analysis. Results showed that damage to the parietal and anterior cingulate cortex was a significant predictor of neglect using CT data (p<0.05), whereas regional blood flow in the parietal cortex was the best predictor of neglect using SPECT data (p<0.05).

Eskes et al. (2003) examined convergent validity of the SNAP by comparison with a measure of generalized attentional capacity (digit span forward minus digit span backward) in a sample of 9 patients with acute to chronic stroke, using Spearman correlation coefficient. Results showed an excellent correlation between measures (r=0.85, p<0.02).

Known groups validity:
Black et al. (1995) administered the SNAP to 294 patients with acute stroke. Comparison of incidence of neglect between patients with right hemisphere damage vs. patients with left hemisphere damage was 54% vs. 31% (respectively). Performance on SNAP subtests differed significantly between groups: Shape cancellation: 74% vs. 54% (respectively); Line bisection: 61% vs. 35 % (respectively); Line cancellation: 26% vs. 7% (respectively); and Drawing: 25% vs. 3% (respectively).

Criterion validity:

Concurrent validity:
No studies have reported on concurrent validity of the SNAP among patients with stroke.

Predictive validity:
Leibovitch et al (2012) examined predictive validity of the SNAP by comparison with the visual search board (VSB) visual search task (Kimura, 1986) in a sample of 224 patients with acute stroke, using logistic regression. Comparison of test results showed that the SNAP significantly predicted neglect (present/absent) on the VSB.

Responsiveness

Sensitivity/specificity:
Black et al. (1990) used a modified version of the SNAP in a sample of 41 patients with acute stroke (n=21 with right hemisphere damage). The tool comprised the standard SNAP subtests as well as two additional tasks (designs cancellation, visual search). Results showed that the line bisection task was the most sensitive subtest, with neglect observed in 76% and 30% of individuals with right and left hemisphere damage respectively. While the line bisection subtest was most likely to detect mild impairment, the line drawing and line cancellation subtests indicated more severe impairment.

Black et al (1995) administered the SNAP to 294 patients with acute stroke. Comparison of incidence of neglect between patients with right hemisphere damage vs. left hemisphere damage was 54% vs. 31% (respectively). Results indicate that the shape cancellation subtest was the most sensitive subtest, with neglect observed in 74% and 54% of individuals with right and left hemisphere damage respectively. The line bisection subtest revealed neglect in 61% and 35% of individuals with right and left hemisphere damage respectively.

Leibovitch et al. (2012) evaluated sensitivity and specificity of the SNAP in a sample of 224 patients with acute stroke, using the visual search board (VSB) visual search task (Kimura, 1986) to confirm neglect. Overall, the SNAP showed 68% sensitivity and 76% specificity. The shape cancellation task showed highest sensitivity (70% sensitivity); the drawing/copying tasks showed highest specificity (99% specificity).

References

  • Black, S.E., Vu, B., Martin, D., & Szalai, J.P. (1990). Evaluation of a bedside battery for hemispatial neglect in acute stroke [Abstract]. Journal of Clinical and Experimental Neuropsychology, 12, 109.
  • Black, S., Ebert, P. L., Leibovitch, F., Szalai, J. P., & Blair, N. (1995). Recovery in hemispatial neglect [Abstract]. Neurology, 45(suppl 4), A178.
  • Black, S. E., Leibovitch, F. S., Ebert, P. L., & L., B. K. (2016). SNAP : Sunnybrook Neglect Assessment Procedure Administration and Scoring Manual.
  • Eskes, G.A., Butler, B., McDonald, A., Harrison, E.R., & Phillips, S.J. (2003). Limb activation effects in hemispatial neglect. Archives of Physical Medicine and Rehabilitation, 84, 323-8.
  • Leibovitch, F.S., Black, S.E., Caldwell, C.B., Ebert, P.L., Ehrlich, L.E., & Szalai, J.P. (1998). Brain-behaviour correlations in hemispatial neglect using CT and SPECT: the Sunnybrook stroke study. Neurology, 50, 901-8.
  • Leibovitch, F. S., Vasquez, B. P., Ebert, P. L., Beresford, K. L., & Black, S. E. (2012). A short bedside battery for visuoconstructive hemispatial neglect: Sunnybrook Neglect Assessment Procedure (SNAP). Journal of Clinical and Experimental Neuropsychology, 34(4), 359-68. doi:10.1080/13803395.2011.645016
  • Menon-Nair, A., Korner-Bitensky, N., & Ogourtsova, T. (2007). Occupational Therapists’ identification, assessment, and treatment of unilateral spatial neglect during stroke rehabilitation in Canada. Stroke, 38, 2556-62. DOI: 10.1161/STROKEAHA.107.484857

See The Measure

How to obtain the SNAP

The SNAP administration and scoring manual and test booklet can be accessed here.

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