Abstract
This analysis evaluates the ability of the Standardized Cosmesis and Health Nasal Outcomes Survey to discriminate among different symptom severities and its performance at different severity levels.
The Standardized Cosmesis and Health Nasal Outcomes Survey (SCHNOS) is a new 10-item questionnaire to evaluate the functional and cosmetic outcomes of rhinoplasty.1 The SCHNOS produces 2 scores: obstruction (SCHNOS-O; items 1-4) and cosmesis (SCHNOS-C; items 5-10). The exact psychometric characteristics of the SCHNOS are unknown.1 To confirm that patients with greater symptom severity have a higher probability of achieving a higher score on a questionnaire, a self-administered test can be evaluated by a Rasch or item response theory (IRT) analysis.2 Our objective was to evaluate the psychometric properties of the SCHNOS using IRT analysis to determine its ability to discriminate among different levels of symptom severity and to evaluate its performance at different severity levels.
Methods
A total of 350 consecutive patients completed the SCHNOS during rhinoplasty consultation from June 1, 2017, through February 28, 2018. This is a retrospective study by design; hence, the consent process was waived by the Stanford University Institutional Review Board. The patient data were deidentified before data analysis.
Item response theory analysis defines discrimination and difficulty variables of a questionnaire. A discrimination variable describes the sensitivity of the test to differentiate different severities of symptoms.3,4,5 In turn, the difficulty variable refers to the level of a perceived nasal problem needed to achieve a 50% probability of choosing a particular score.3,4,5
The IRT Rating Scale Model was used. Item information and test characteristic curves and the test information functions were presented graphically. All analyses were performed using Stata/IC Statistical Software, release 15 (StataCorp).
Results
Of the 350 patients, 140 (40.0%) were men, and the mean (SD) age was 38.0 (14.1) years. The mean (SD) SCHNOS-O score was 48.3 (31.8), and the mean (SD) SCHNOS-C score was 33.6 (30.6).
The discrimination abilities of SCHNOS-O and SCHNOS-C were perfect, with values of 1.93 (95% CI, 1.67-2.19; P < .001) for SCHNOS-O and 1.66 (95% CI, 1.45-1.88; P < .001) for SCHNOS-C. Almost each step up or down across the scale was associated with a meaningful difference in severity of the measured nasal problem perceived by a patient (Table). In SHNOS-O, the mean difficulty variable of each item was associated with the midpoint of the scale. When analyzing the difficulty variable for SCHNOS-C items, the patients tended to underestimate the severity of their experienced cosmetic disadvantage. For the entire SCHNOS-O score, most information could be obtained around the mean level of the perceived problem (Figure). The curve of SCHNOS-C was shifted toward greater severity of symptoms.
Table. Difficulty Coefficients of SCHNOS Items.
| SHNOS Item | Coefficient (95% CI) | P Value |
|---|---|---|
| Item 1 | ||
| 1 vs 0 | −0.35 (−0.52 to −0.19) | <.001 |
| 2 vs 1 | −0.33 (−0.50 to −0.15) | <.001 |
| 3 vs 2 | −0.18 (−0.34 to −0.01) | .03 |
| 4 vs 3 | 0.37 (0.22 to 0.53) | <.001 |
| 5 vs 4 | 1.18 (0.99 to 1.37) | <.001 |
| Item 2 | ||
| 1 vs 0 | −0.33 (−0.49 to −0.16) | <.001 |
| 2 vs 1 | −0.3 (−0.47 to −0.13) | .001 |
| 3 vs 2 | −0.15 (−0.31 to 0.01) | .07 |
| 4 vs 3 | 0.4 (0.24 to 0.56) | <.001 |
| 5 vs 4 | 1.21 (1.02 to 1.4) | <.001 |
| Item 3 | ||
| 1 vs 0 | −0.43 (−0.6 to −0.27) | <.001 |
| 2 vs 1 | −0.41 (−0.58 to −0.23) | <.001 |
| 3 vs 2 | −0.26 (−0.42 to −0.09) | .002 |
| 4 vs 3 | 0.29 (0.14 to 0.45) | <.001 |
| 5 vs 4 | 1.1 (0.92 to 1.28) | <.001 |
| Item 4 | ||
| 1 vs 0 | −0.41 (−0.57 to −0.24) | <.001 |
| 2 vs 1 | −0.38 (−0.55 to −0.2) | <.001 |
| 3 vs 2 | −0.23 (−0.39 to −0.07) | .006 |
| 4 vs 3 | 0.32 (0.17 to 0.47) | <.001 |
| 5 vs 4 | 1.13 (0.94 to 1.31) | <.001 |
| Item 5 | ||
| 1 vs 0 | 0.46 (0.3 to 0.62) | <.001 |
| 2 vs 1 | 0.33 (0.16 to 0.49) | <.001 |
| 3 vs 2 | 0.31 (0.14 to 0.47) | <.001 |
| 4 vs 3 | 0.98 (0.8 to 1.16) | <.001 |
| 5 vs 4 | 1.38 (1.17 to 1.59) | <.001 |
| Item 6 | ||
| 1 vs 0 | 0.48 (0.32 to 0.65) | <.001 |
| 2 vs 1 | 0.35 (0.18 to 0.52) | <.001 |
| 3 vs 2 | 0.33 (0.17 to 0.5) | <.001 |
| 4 vs 3 | 1.01 (0.83 to 1.19) | <.001 |
| 5 vs 4 | 1.4 (1.2 to 1.61) | <.001 |
| Item 7 | ||
| 1 vs 0 | 0.28 (0.12 to 0.43) | .001 |
| 2 vs 1 | 0.15 (−0.02 to 0.31) | .08 |
| 3 vs 2 | 0.13 (−0.04 to 0.29) | .13 |
| 4 vs 3 | 0.8 (0.63 to 0.98) | <.001 |
| 5 vs 4 | 1.2 (1 to 1.4) | <.001 |
| Item 8 | ||
| 1 vs 0 | 0.27 (0.11 to 0.42) | .001 |
| 2 vs 1 | 0.13 (−0.03 to 0.3) | .12 |
| 3 vs 2 | 0.11 (−0.05 to 0.28) | .18 |
| 4 vs 3 | 0.79 (0.62 to 0.96) | <.001 |
| 5 vs 4 | 1.19 (0.99 to 1.38) | <.001 |
| Item 9 | ||
| 1 vs 0 | 0.41 (0.25 to 0.57) | <.001 |
| 2 vs 1 | 0.28 (0.11 to 0.44) | .001 |
| 3 vs 2 | 0.26 (0.09 to 0.42) | .002 |
| 4 vs 3 | 0.94 (0.76 to 1.11) | <.001 |
| 5 vs 4 | 1.33 (1.13 to 1.53) | <.001 |
| Item 10 | ||
| 1 vs 0 | 0.23 (0.07 to 0.38) | .005 |
| 2 vs 1 | 0.09 (−0.07 to 0.26) | .27 |
| 3 vs 2 | 0.07 (−0.09 to 0.24) | .38 |
| 4 vs 3 | 0.75 (0.58 to 0.92) | <.001 |
| 5 vs 4 | 1.15 (0.95 to 1.34) | <.001 |
Abbreviation: SHNOS, Standardized Cosmesis and Health Nasal Outcomes Survey.
Figure. Standardized Cosmesis and Health Nasal Outcomes Survey (SCHNOS) Characteristic Information Curves for Obstruction (SCHNOS-O) and Cosmesis (SCHNOS-C).
Characteristic (A) and information (B) curves for SCHNOS-C and SCHNOS-O.
Discussion
The SCHNOS demonstrated overall perfect ability to distinguish different levels of perceived nasal symptoms. The SCHNOS-O score was effective at differentiating between patients with and without symptoms, whereas the SCHNOS-C score was most effective when discriminating symptoms at higher severity levels. Although the sample was large, it was limited to one university clinic with predominantly younger and female patients. Thus, similar studies should be completed in other settings.
The high similarity between information curves and difficulty estimates of different items of the SCHNOS may signal redundancy in items on the scale. This possibility can be tested with confirmatory factor analysis in a subsequent study.
Both the SCHNOS-O and SCHNOS-C had perfect discrimination ability. The SCHNOS-O demonstrates ideal results regarding its capability to distinguish patients with even mild nasal obstruction from those without obstruction. As such, the SCHNOS-O may serve as both a screening and clinical tool for nasal obstruction. The SCHNOS-C was especially effective among patients with more severe perceived cosmetic disadvantages; thus, it is probably more reliable as a clinical rather than a screening tool.
References
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