Statistical methods for assessing agreement between double readings of clinical measurements

Statistical analysis of data is crucial in cephalometric investigations. There are certainly excellent examples of good statistical practice in the field, but some articles published worldwide have carried out inappropriate analyses. OBJECTIVE: The purpose of this study was to show that when the double records of each patient are traced on the same occasion, a control chart for differences between readings needs to be drawn, and limits of agreement and coefficients of repeatability must be calculated. MATERIAL AND METHODS: Data from a well-known paper in Orthodontics were used for showing common statistical practices in cephalometric investigations and for proposing a new technique of analysis. RESULTS: A scatter plot of the two radiograph readings and the two model readings with the respective regression lines are shown. Also, a control chart for the mean of the differences between radiograph readings was obtained and a coefficient of repeatability was calculated. CONCLUSIONS: A standard error assuming that mean differences are zero, which is referred to in Orthodontics and Facial Orthopedics as the Dahlberg error, can be calculated only for estimating precision if accuracy is already proven. When double readings are collected, limits of agreement and coefficients of repeatability must be calculated. A graph with differences of readings should be presented and outliers discussed

Comparison of cephalometric measurements from three radiological clinics Comparação de grandezas cefalométricas obtidas em três clínicas radiológicas

The orthodontic documentation carried out in radiological clinics is essential for diagnosis, planning and control of the orthodontic treatment. Amongst the diagnosis elements used are the cephalometric measurements, and errors can be incorporated as they are obtained. The objective of this work was to evaluate the values of some cephalometric measurements obtained in three radiological clinics using 30 lateral cephalometric radiographs of the head randomly chosen from the archives of the Department of Child Dentistry (Discipline of Orthodontics), School of Dentistry of Piracicaba, UNICAMP. These values were compared with the measurements obtained manually (control group) using variance analysis and Tukey’s and Friedman’s tests. Of the fourteen cephalometric measurements evaluated, the results demonstrated that only four of them presented statistically significant differences: IMPA, 1-NA, FMA, and H-nose. We concluded that although the majority of the mean cephalometric values did not present statistically significant differences, a great variability in the results was found when all the radiographic values were compared. This variability may influence the interpretation of the cephalometric measurements. Hence, we suggest that when the practitioner receives orthodontic documentation, he/she should redo the cephalometric analysis and compare the measurement values found with those presented to him. In addition, the practitioner should be prepared to use other elements for diagnosis, planning and control of the orthodontic treatment.<br>A documentação ortodôntica realizada em clínicas radiológicas é essencial para diagnóstico, planejamento e controle do tratamento ortodôntico. Dentre os elementos de diagnóstico utilizados estão as grandezas cefalométricas, e erros podem ser incorporados durante a obtenção das mesmas. O objetivo deste trabalho foi avaliar os valores de algumas grandezas cefalométricas obtidas em três clínicas radiológicas, utilizando-se 30 telerradiografias da cabeça em norma lateral, escolhidas ao acaso, do arquivo do Departamento de Clínica Infantil (Disciplina de Ortodontia) da Faculdade de Odontologia de Piracicaba - UNICAMP. Esses valores foram comparados com os das grandezas obtidas manualmente (grupo controle), utilizando-se a análise de variância e os testes de Tukey e Friedman. Os resultados demonstraram que das 14 medidas cefalométricas avaliadas, apenas 4 apresentaram diferenças estatisticamente significantes: IMPA, 1-NA, FMA, e H-nariz. Concluímos que apesar de a maioria dos valores médios das grandezas cefalométricas não apresentarem diferenças estatisticamente significantes, ao compararmos todos os valores obtidos em cada uma das radiografias, encontramos grande variabilidade nos resultados, o que pode interferir na interpretação das grandezas cefalométricas. Assim, os autores sugerem ao ortodontista, quando receber a documentação ortodôntica, realizar novamente as análises cefalométricas para comparar os valores das grandezas, e utilizar outros elementos para diagnóstico, planejamento e controle do tratamento ortodôntico