How to report reliability in orthodontic research: Part 1.

In reporting reliability, duplicate measurements are often needed to determine if measurements are sufficiently in agreement among the observers (interobserver agreement) and/or within the same observer (intraobserver agreement). Some reports are often analyzed inappropriately using paired t tests and/or correlation coefficients. The aim of this article is to highlight the statistical problems of reliability testing using paired t tests and correlation coefficients and to encourage good reliability reporting within orthodontic research. With regard to the complex issue of reliability, a simple and singular statistical approach is not available. However, some methods are better than others. A graphic technique based on the Bland-Altman plot that can be simultaneously applied for both intra- and interobserver reliability will also be discussed.