Sunnybrook Neglect Assessment Procedure (SNAP)

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