Spearman–Brown prophecy formula and Cronbach's alpha: different faces of reliability and opportunities for new applications

Objectives There are similarities between the different forms of reliability, such as internal consistency (internal reliability) and interrater and intrarater reliability. Reliability coefficients that are based on classical test theory can be expressed as intraclass correlation coefficients (ICCs), such as Cronbach's alpha. The Spearman–Brown prophecy formula (SB formula) is used to calculate the reliability when the number of items in a questionnaire is changed. This paper aims to increase insight into reliability studies by pointing to the assumptions of reliability coefficients, similarities between various coefficients, and the subsequent new applications of reliability coefficients. Design, Settings and Results The origin and assumptions of Cronbach's alpha and the SB formula are discussed. Cronbach's alpha is written as an ICC formula, using the well-known property that taking the average value of a number of ratings increases the reliability of a measurement. We illustrate with an example that the ICC formulas for average measurements of multiple raters and the SB formula give similar results. This implies that the SB formula can be used to decide on the number of measurements to be averaged and thus on the number of raters required, for obtaining measurements with acceptable reliability, even if the variance components of the ICC formula are not known. Using the same example, we illustrate the principle of “Cronbach's alpha if item deleted” to decide on the poorest performing raters in a set of raters. Conclusion These applications have different assumptions: the principle of “Cronbach's alpha if item deleted” is based on the assumption of a fixed set of items/raters and the SB formula is based on the assumption of random raters. The example also emphasizes the need for more raters in the design of the reliability study to obtain a robust estimation of reliability

Aesthetics Assessment and Patient Reported Outcome of Nasolabial Aesthetics in 18-Year-Old Patients With Unilateral Cleft Lip

Objective: To determine if there is a correlation between objective nasolabial aesthetics assessment using the Cleft Aesthetic Rating Scale (CARS) and patient satisfaction. Design: Retrospective analysis of a generic satisfaction questionnaire and independent assessment by three cleft surgeons of the nasolabial area of these patients on 2D frontal photographs, using the CARS. Setting: The Vrije Universiteit Medical Center and The Academic Center for Dentistry Amsterdam. Patients: Thirty-nine 18-year old patients with a repaired complete or incomplete unilateral cleft lip, with or without a cleft palate, and a completed satisfaction questionnaire. Exclusion criteria were an incomplete questionnaire; a history of facial trauma; and congenital syndromes affecting facial appearance. Main Outcome Measures: The correlation between surgeon evaluation (on a 5-point Likert scale) and patient satisfaction (not, moderately or very satisfied) on nasolabial appearance was assessed using Spearman rho (ρ). Results: There was a negligible correlation between surgeon evaluation and patient satisfaction on nose assessment (ρ = 0.20) and a moderate correlation on lip assessment (ρ = 0.32). Conclusions: Most literature supports this discrepancy between different objective aesthetics evaluation methods and subjective patient-reported outcome measures, suggesting there are factors playing a role in patient satisfaction that are impossible to objectify with assessment methods. Therefore, a strong emphasis should remain on clear communication between the physician and patient regarding their expectations, perception, and satisfaction of surgery results

Atypical Outcomes of Nasal and Lip Appearance After Unilateral Cleft Lip Repair: Judgment by Professionals, Patients, and Laypeople

Objective: To gain more insight into the assessment of “atypical” nasal and lip appearance outcomes compared to “typical” appearance outcomes after unilateral cleft lip and palate (UCLP) repair, when judged by professionals, patients with repaired UCLP, and laypeople. Design: An online survey containing 3 series of photographs with various degrees of “typical” and “atypical” nasal and lip appearance outcomes after UCLP repair was sent to 30 professionals, 30 patients with repaired UCLP, and 50 laypeople in 2 countries. Participants were instructed to rank the photographs from excellent to poor based on overall appearance. Mean rank positions of photographs were analyzed and differences in mean rank score between “typical” and “atypical” results were assessed using a T-test. Agreement of ranking between the 3 groups was assessed with an analysis of variance analysis. Setting: Amsterdam UMC, location VUmc, Netherlands and Boston Children’s Hospital, Boston, USA. Patients: Photographs of 6- to 18-year-old patients with repaired UCLP. Results: “Atypical” appearance outcomes were ranked significantly less favorably (small nostril: P = 0.00; low vermillion border: P = 0.02; whistling deformity: P = 0.00) compared to “typical” outcomes. Difference between professionals, patients and laypeople in rank positioning the photographs was not statistically significant (P = 0.89). Conclusions: Noses with a smaller nostril and lips containing a whistling deformity were perceived as poorer outcome compared to the “typical” results. Professionals, patients, and laypeople are in agreement when assessing these outcomes

Development of the submental nasal appearance scale for the assessment of repaired unilateral complete cleft lip: A pilot study

Objective: To develop the “Submental Nasal Appearance Scale” (SNAS), which is an easy-to-use objectified tool to represent a cleft surgeon’s standard for assessment of the nasal appearance from the submental perspective. Design: Eighty-five photographs of patients with unilateral complete cleft lip and palate were selected and cropped, displaying the submental view. Sixty-one photographs were used to develop 5 sets of reference photographs. Three cleft surgeons graded 24 photographs with these sets and subjectively graded the overall nasal appearance as well. Internal agreement for both methods was calculated, as well as correlation between them. The SNAS was created, by only using the combination of sets that showed the highest reliability and correlation. Setting: Boston Children’s Hospital, Boston, Massachusetts. Patients: Six-to 9-year-old patients with unilateral complete cleft lip and palate. Results: The intrarater and interrater reliability was 0.84 and 0.79, respectively, for the SNAS and 0.76 and 0.62, respectively, for the overall appearance assessment. The correlation was 0.74 between the methods. Conclusions: The SNAS is a reliable tool that reflects a cleft surgeon’s standard and could be used independently or in combination with existing rating scales using the frontal and/or lateral view, for assessment after cleft lip repair