Page 120 - REV T-I JOURNAL INTERIOR ISSUU 18 2-3

196 HIGHSMITH ET AL.

In the above equation for sensitivity, n HAI score 10 of each instrument, respectively. Data were compared
represents the number of subjects who scored 10 for both tests for ascending and descending condi-
on the HAI because the rater found them to have an tions. Intraclass correlation coefficients (ICC) were
n
asymmetrical step length, and |DoA|>0.1 represents the determined using Spearman’s Rho. Definitions for
number of subjects who truly exhibited asymmetri- correlation strength also vary (15,18-20). We inter-
cal steps as assessed with video motion analysis and preted 0.9 to 1.0 as an excellent correlation, 0.75 to
the DoA equation for step length symmetry. In the 0.89 a good correlation, 0.5 to 0.74 an adequate cor-
n
above equation for specificity, HAI score 11 represents relation, and below 0.5 a poor correlation. The level
the number of subjects who scored 11 on the HAI for statistical significance was determined a priori to
because the rater found them to have symmetrical be p ≤ 0.05.
n
step length, and |DoA|≤0.1 represents the number of
subjects who truly did exhibit symmetrical steps as RESULTS
assessed with video motion analysis and the DoA Twenty (n = 20) individuals with TFA completed
equation for step length symmetry. Higher levels of the study. The sample was 80% male with etiology
sensitivity and specificity provide evidence to support of trauma (70%), tumor (20%), or vascular disease
the validity of the HAI to assess step length symmetry (10%). Mean (SD) age was 46.5 years of age (±14.2).
walking on ramps. To evaluate levels of sensitivity All subjects were unlimited community ambulators.
and specificity, we interpreted scores from 90% to Sensitivity of the HAI was calculated at 88.0% for
100% as excellent, 75% to 89% as good, 50% to 74% uphill and 94.0% for downhill conditions. These
as adequate, and below 50% as poor sensitivity and results correspond to positive likelihood ratios of
specificity for the HAI uphill and downhill. 3.5 and 2.8, respectively. Specificity for the instrument
Positive and negative likelihood ratios can be cal- was determined to be 75.0% for uphill and 67.0%
culated from the sensitivity and specificity values. A for downhill. These results correspond to negative
positive likelihood ratio indicates how many times
more likely a positive test will be seen in those with likelihood ratios of 0.17 and 0.10, respectively. These
more symmetric step lengths than in those with less results are summarized in Table 1.
symmetric step lengths (15). Interpretation of like- For the HAI, Spearman Rho ICCs of r s = 0.80 (p
lihood ratios vary (16,17). We interpreted a positive < 0.001) for uphill and 0.67 (p = 0.001) for downhill
likelihood ratio of 10 or more as large, 5 to 9.94 as conditions between rater one and rater two were
moderate, 2 to 4.94 as small, and 1 to 1.94 as very found. ICCs of r s = 0.87 (p < 0.001) and 0.73 (p <
small positive likelihood. These positive likelihood 0.001) were calculated between initial and repeat
ratios were used to determine if the HAI was a very testing scores for uphill and downhill conditions,
useful, often useful, sometimes useful, or rarely useful respectively (Table 2). Mean (SD) uphill times (Table
test, respectively. A negative likelihood ratio, then, 3), in seconds, for trials one, two, and three were
indicated how many times more likely a negative test 4.71 (0.86), 4.71 (0.99), and 4.72 (1.03), respectively,
will be seen in those with more step length symmetry resulting in a mean percent difference of 0.11% among
compared to those with less step length symmetry trials. Mean and median scores were 10.8 and 11 for
(15). A negative likelihood ratio of less than 0.1 was all trials. Mean downhill times, in seconds, for trials
interpreted as large, 0.11 to 0.2 as moderate, 0.21 to one, two, and three were 4.80 (1.14), 4.74 (1.19), and
0.5 as small, and 0.51 to 1.0 as very small negative 4.78 (1.40), respectively, resulting in a mean percent
likelihood. These negative likelihood ratios were used difference of 1.1% among trials. Mean and median
to determine if the HAI was a very useful, often useful, downhill scores were 10.9 and 11 for all trials.
sometimes useful, or rarely useful test, respectively. For the SAI, ICCs of rs = 1.00 (p < 0.001) and 0.89
Comparisons between rater one and rater two at (p < 0.001) were found between raters one and two for
initial testing and rater one at the repeat evaluation ascending and descending conditions, respectively.
were made to assess inter- and intra-rater reliability ICCs of rs = 1.00(p < 0.001) were calculated for both