Table 4
Rotated Component Matrices for three exploratory structure analyses.
Item | Principal axis | Principal components | Unweighted least squares |
| Factor 1 | Factor 2 | Factor 1 | Factor 2 | Factor 1 | Factor 2 |
1. I like to use [X] frequently. | .450 | − .129 | .608 | .030 | .450 | − .127 |
2. I find [X] unnecessarily complex. | − .572 | .380 | − .651 | .340 | − .575 | .375 |
3. I think [X] is easy to use. | .782 | − .157 | .789 | − .157 | .781 | − .156 |
4. I need the support of an expert consultant to be able to use [X]. | − .182 | .751 | − .209 | .785 | − .182 | .759 |
5. I find the various components of [X] are well integrated. | .646 | − .080 | .738 | .001 | .646 | − .078 |
6. I think there is too much inconsistency in [X]. | − .384 | .383 | − .427 | .450 | − .387 | .377 |
7. I would imagine that most people would learn to use [X] very quickly. | .534 | − .138 | .579 | − .173 | .534 | − .137 |
8. I find [X] very cumbersome to use. | − .622 | .405 | − .671 | .393 | − .626 | .400 |
9. I feel very confident using [X]. | .596 | − .306 | .667 | − .279 | .596 | − .305 |
10. I needed to learn a lot of things before I could get going with [X]. | − .087 | .478 | .023 | .805 | − .089 | .477 |
N = 205. |
Ius Factor Structure
Examining the point of inflection on a scree plot indicated that a two-factor solution for the IUS best fit the data. Factor 1 had an eigenvalue of 4.0 and accounted for 40.5% of the variance, and Factor 2 had an eigenvalue of 1.2 and accounted for 12.1% of the variance, for a total of 52.6% of variance accounted for in the two-factor solution. For all three approaches to analysis, items 1, 2, 3, 5, 7, 8, and 9 loaded onto the first factor, whereas items 4 and 10 loaded onto the second. Item 6, “I think there is too much inconsistency in [intervention],” loaded almost equally onto both factors, and was therefore removed from later subscale analyses. See Table 4 for the rotated component matrix. The item-factor alignment was nearly identical to that of Lewis and Sauro[17], which found a two-factor structure, but inconsistent with studies that followed[26]. Therefore, we named these factors the same as in the 2009 study[17]; “Usable” and “Learnable.” To place the Usable and Learnable scores on a comparable 0 to 100 scale as the Overall IUS score, we multiplied their summed score contributions by 3.57 and 12.50, respectively.
Scale Correlations
The correlations between the subscales and the Overall IUS score were r = .957 for Usable (p < .001) and r = .630 for Learnable (p < .001). The strong scale-to-total correlation for Usable was expected, given that 7 out of 9 items were included in this subscale. The correlation between Usable and Learnable was moderate at r = .377 (p < .001).
Reliability/internal Consistency
The overall IUS items had good internal consistency (α = .83). Coefficient alphas for Usable and Learnable were α = .82 and α = .63, respectively. Only two items loaded onto Learnable, contributing to its low alpha. The Learnable subscale did not have sufficient reliability to meet the typical minimum standard of .70[32, 33].
Sensitivity
Intervention type. The majority of providers (83.9%) reported most commonly using MI, with the next largest group (9.3%) reporting that they used CBT (Table 1). We conducted an ANOVA with most commonly delivered intervention as an independent variable with 3 levels (MI, CBT, and other). ANOVAs revealed significant differences by type of intervention on the Total IUS score and the Usable subscale. MI and CBT appeared to be less usable than the aggregated list of other types of therapy. The average adjusted IUS score for those who delivered MI was 69.1, CBT was 71.7, and “other” was 81.8 (F(2, 202) = 6.06; p = .003). The average score on the adjusted Usable subscale for those who deliver MI was 68.8, CBT was 73.5, and “other” was 83.9 (F(2, 202) = 7.93; p < .001). There were no significant differences between intervention types on the Learnable subscale: for those delivering MI the average score was 70.0; CBT was 65.1, and “Other” was 74.1 (F(2, 202) = 0.93; p = .397).
Professional role. There were significant differences on the overall IUS and the Usable subscale depending on the respondent’s professional role. Behavioral health providers (M = 77.2) had higher scores than both medical providers (M = 68.5) and pharmacists (M = 66.0) on the overall IUS (F(2,192) = 7.30; p = .001). Behavioral health providers (M = 79.0) also scored significantly higher on the Usable subscale compared to medical providers (M = 68.0) and pharmacists (M = 66.2; F(2, 192) = 9.93; p < .001). There were no significant differences between behavioral health providers (M = 70.6), medical providers (M = 69.9) and pharmacists (M = 64.8) on the Learnable subscale (F(2, 192) = 0.40; p = .670).
Distribution Of Ius Subscale Scores
Table 5 shows descriptive statistics on distributions of scores on the IUS, alongside a comparison with prior SUS data[17]. Of note, the current sample had significantly higher overall scores (t = 8.58; p < .001) and Usable scores (t = 10.63; p < .001) on average, whereas the 2009 SUS study had slightly yet significantly higher Learnable scores (t = -2.16; p = .032).
Table 5
Comparison with prior System Usability Scale data.
| Lewis & Sauro SUS (comparison sample) | Current Dataset |
Statistic | Overall | Usable | Learnable | Overall | Usable | Learnable |
N | 324 | 324 | 324 | 205 | 205 | 205 |
Minimum | 7.5 | 0.0 | 0.0 | 30.58 | 32.13 | 0.00 |
Maximum | 100 | 100 | 100 | 100 | 100 | 100 |
Mean | 62.10 | 59.40 | 72.70 | 70.33** | 70.25** | 69.81* |
Variance | 494.38 | 531.54 | 674.47 | 184.11 | 212.68 | 365.24 |
Standard Deviation | 22.24 | 23.06 | 25.97 | 13.57 | 14.58 | 19.13 |
Standard Error | 1.24 | 1.28 | 1.44 | 0.95 | 1.01 | 1.32 |
Skewness | − .42 | − .38 | − .80 | − .11 | − .18 | − .55 |
Kurtosis | N/A | N/A | N/A | − .11 | − .18 | − .55 |
*Significantly different from comparison sample at p = .05; **Significantly different from comparison sample at p = .001. |