Small sample size limits the usefulness of anterior open bite study

Abstract

We read the article by Akan et al evaluating anterior open bite correction in the October 2020 issue with great interest (Akan B, Ünal B, Şahan A, Kızıltekin R. Evaluation of anterior open bite correction in patients treated with maxillary posterior segment intrusion using zygomatic anchorage. Am J Orthod Dentofacial Orthop 2020;158:547-54). However, we would like to discuss certain points. The authors have not described the limitations of the study. They calculated the sample size from the study of Erverdi et al,1Erverdi N. Keles A. Nanda R. The use of skeletal anchorage in open bite treatment: a cephalometric evaluation.Angle Orthod. 2004; 74: 381-390PubMed Google Scholar which itself shows a compromised sample size of only 10 subjects. The sample size calculated for the present study was 14 because the effect size taken by the authors was 1.09, which was obtained from the previous study.1Erverdi N. Keles A. Nanda R. The use of skeletal anchorage in open bite treatment: a cephalometric evaluation.Angle Orthod. 2004; 74: 381-390PubMed Google Scholar The authors should have taken a medium effect size of 0.5 for calculating the sample size because the previous study was a compromised sample size study. If we take 0.5 as the effect size for sample size calculation with 95% power and 5% alpha, it will give a result of 45 samples. If we perform the power analysis of the present study with 19 samples and the effect size as 0.5, then the power of the study comes out to be only 67%. Small sample size is evident from Table II, in which certain parameters show a standard deviation greater than the mean. According to Altman,2Altman D.G. Practical statistics for medical research. Chapman & Hall, London, United Kingdom1991Google Scholar the data do not follow a normal distribution (standard deviation greater than mean), and therefore, a nonparametric test should have been used instead of a parametric paired t test. Although the study is very interesting and clinically important, when presenting the results, the authors should also discuss the limitations of the study. Evaluation of anterior open bite correction in patients treated with maxillary posterior segment intrusion using zygomatic anchorageAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 158Issue 4PreviewThis study aimed to investigate dentofacial changes in patients treated with maxillary molar intrusion with zygomatic anchors. Full-Text PDF Authors' responseAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 159Issue 3PreviewThank you very much for reading and criticizing our study in such detail.1 Because measurements were taken from the same subjects from dependent groups, many genetic and even epigenetic factors were eliminated. When the simulation is made from dependent groups according to the effect width stated before, the following results are obtained. Probably, the situation you are criticizing may be due to other package programs or different factors.2-5 Full-Text PDF